[WFS/OGCAPI] In source select dialog box, better handle list of CRS

- Use an orderered list instead of a set, so that the first element
  is really the preferred one
- Do not trust the project CRS if the project has no layers: it is
  better to rely on the preferred CRS of the source instead

src/providers/wfs/qgswfssourceselect.cpp

@@ -176,35 +176,33 @@ void QgsWFSSourceSelect::populateConnectionList()
   changeConnection();
 }
 
-QString QgsWFSSourceSelect::getPreferredCrs( const QSet<QString> &crsSet ) const
+QString QgsWFSSourceSelect::getPreferredCrs( const QList<QString> &crsList ) const
 {
-  if ( crsSet.size() < 1 )
+  if ( crsList.size() < 1 )
   {
     return QString();
   }
 
-  //first: project CRS
-  QgsCoordinateReferenceSystem projectRefSys = QgsProject::instance()->crs();
-  //convert to EPSG
-  QString ProjectCRS;
-  if ( projectRefSys.isValid() )
+  //first: project CRS (if the project is not empty)
+  QgsProject *project = QgsProject::instance();
+  if ( !project->mapLayers().isEmpty() )
   {
-    ProjectCRS = projectRefSys.authid();
-  }
-
-  if ( !ProjectCRS.isEmpty() && crsSet.contains( ProjectCRS ) )
-  {
-    return ProjectCRS;
-  }
+    QgsCoordinateReferenceSystem projectRefSys = QgsProject::instance()->crs();
+    //convert to EPSG
+    QString projectCRS;
+    if ( projectRefSys.isValid() )
+    {
+      projectCRS = projectRefSys.authid();
+    }
 
-  //second: WGS84
-  if ( crsSet.contains( geoEpsgCrsAuthId() ) )
-  {
-    return geoEpsgCrsAuthId();
+    if ( !projectCRS.isEmpty() && crsList.contains( projectCRS ) )
+    {
+      return projectCRS;
+    }
   }
 
-  //third: first entry in set
-  return *( crsSet.constBegin() );
+  //otherwise: first entry in set
+  return crsList[0];
 }
 
 void QgsWFSSourceSelect::refresh()
@@ -705,7 +703,7 @@ void QgsWFSSourceSelect::changeCRSFilter()
       mProjectionSelector = new QgsProjectionSelectionDialog( this );
 
       mProjectionSelector->setOgcWmsCrsFilter( crsNames );
-      QString preferredCRS = getPreferredCrs( crsNames ); //get preferred EPSG system
+      QString preferredCRS = getPreferredCrs( *crsIterator ); //get preferred EPSG system
       if ( !preferredCRS.isEmpty() )
       {
         QgsCoordinateReferenceSystem refSys = QgsCoordinateReferenceSystem::fromOgcWmsCrs( preferredCRS );

src/providers/wfs/qgswfssourceselect.h

@@ -80,15 +80,14 @@ class QgsWFSSourceSelect: public QgsAbstractDataSourceWidget, private Ui::QgsWFS
     QString mVersion;
 
     /**
-     * Returns the best suited CRS from a set of authority ids
+     * Returns the best suited CRS from a list of authority ids
      *
-     * 1. project CRS if contained in the set
-     * 2. WGS84 if contained in the set
-     * 3. the first entry in the set else
+     * 1. project CRS if contained in the list and the project is not empty
+     * 2. the first entry in the list else
      *
      * \returns the authority id of the crs or an empty string in case of error
     */
-    QString getPreferredCrs( const QSet<QString> &crsSet ) const;
+    QString getPreferredCrs( const QList<QString> &crsList ) const;
 
     void showHelp();