Validate start of modal with Jquery

$(".btn").click(function(e) {
  if ($("#gg").val() == 0 && $("#ggg").val() == 0) {
    alert("Seleccione una opcion antes de continuar");
    return false;
  }
});

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<div class="row">
  <div class="col-md-12">
    <div class="box box-primary">
      <div class="box-header">
        <h4 class="box-title">
        </h4>
      </div>
      <div class="box-body">
        <div id="primero"></div>
        <div class="sonata-ba-collapsed-fields">


          <div class="col-md-3">
            <div class=" sonata-ba-field sonata-ba-field-standard-natural  ">
              <select id="gg" value=0>
                                                 <option value=0 >seleccione</option>
                                                <option value="volvo">Volvo</option>
                                                <option value="saab">Saab</option>
                                                <option value="mercedes">Mercedes</option>
                                                <option value="audi">Audi</option>
                                        </select>
            </div>
            <div>
              <select id="ggg" value=0>
                                        <option value=0 >seleccione</option>
                                        <option value=1>bueno</option>
                                        <option value=2>malo</option>
                                        <option value=3>regular</option>
                                        <option value=4>excelente</option>
                                    </select>
            </div>


            <div class="row-fluid" style="margin-top: 10px;">
              <div class="span12" align="right">
                <button type="button" class="btn btn-success btn-sm" data-toggle="modal" data-target="#miModal"><i class="fa fa-plus-circle" aria-hidden="true"></i> Agregar Detalle</button>

              </div>
            </div>




            <!-- Codigo para lanzar la modal -->
            <div class="modal fade" id="miModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
              <div class="modal-dialog" role="document">
                <div class="modal-content">
                  <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                <span aria-hidden="true">&times;</span>
            </button>
                    <h4 class="modal-title" id="myModalLabel">Agregar Criadero</h4>
                  </div>
                  <form id="newCriadero" action="javascript:void(0);">
                    <div class="modal-body">
                      <div class="box box-primary">
                        <div class="row">
                          <div class="box-header">
                            <h4 class="box-title">
                            </h4>
                          </div>
                          <div class="box-body">
                            <div class="col-md-4">
                              <div class="form-group has-feedback">
                                <div class="input-group">
                                  <label>Canton:</label>
                                  <input type="text" class="form-control" id="canton" name="canton" required>
                                </div>
                                <span class="glyphicon form-control-feedback" aria-hidden="true"></span>
                              </div>
                              <div class="form-group has-feedback">
                                <div class="input-group">
                                  <label>Casas Inspeccionadas:</label>
                                  <input type="number" class="form-control" id="casa_insp" name="casa_insp" required/>
                                </div>

                              </div>
                              <div class="form-group">
                                <label>Casas Positivas:</label>
                                <input type="number" class="form-control" id="casa_pos" name="casa_pos" required>
                              </div>
                              <div class="form-group">
                                <label>Total Instradomiciliar:</label>
                                <input type="number" class="form-control" id="total_intra" name="total_intra">
                              </div>
                              <div class="form-group">
                                <label>Total Anopheles Instradomiciliar:</label>
                                <input type="number" class="form-control" id="anopheles_intra" name="anopheles_intra">
                              </div>

                            </div>
                          </div>
                        </div>
                      </div>
                    </div>
                    <div class="modal-footer">
                      <button type="button" class="btn btn-secondary" data-dismiss="modal">Cerrar</button>
                      <button type="submit" class="btn btn-success" id="agregarDetalle" name="agregarDetalle">Agregar</button>
                    </div>
                  </form>
                </div>
              </div>
            </div>