[bugfix] offline editing converting offline twice

Fixes #10537: Converting offline twice within the same
instance causing unusable offline state.

The problem was due to spatialite connection not being
invalidated.  When the new offline layer is re-created
the provider connection doesn't pick the latest commits.

Funded by Boundless

(cherry-picked from f045492)

src/core/qgsofflineediting.cpp

@@ -287,11 +287,14 @@ void QgsOfflineEditing::synchronize()
           showWarning( remoteLayer->commitErrors().join( "\n" ) );
         }
       }
-
+      // Invalidate the connection to force a reload if the project is put offline
+      // again with the same path
+      offlineLayer->dataProvider()->invalidateConnections( QgsDataSourceURI( offlineLayer->source() ).database() );
       // remove offline layer
       QgsMapLayerRegistry::instance()->removeMapLayers(
         ( QStringList() << qgisLayerId ) );
 
+
       // disable offline project
       QString projectTitle = QgsProject::instance()->title();
       projectTitle.remove( QRegExp( " \\(offline\\)$" ) );
@@ -459,6 +462,7 @@ QgsVectorLayer* QgsOfflineEditing::copyVectorLayer( QgsVectorLayer* layer, sqlit
     return nullptr;
 
   QString tableName = layer->id();
+  QgsDebugMsg( QString( "Creating offline table %1 ..." ).arg( tableName ) );
 
   // create table
   QString sql = QString( "CREATE TABLE '%1' (" ).arg( tableName );
@@ -541,9 +545,10 @@ QgsVectorLayer* QgsOfflineEditing::copyVectorLayer( QgsVectorLayer* layer, sqlit
   if ( rc == SQLITE_OK )
   {
     // add new layer
-    QgsVectorLayer* newLayer = new QgsVectorLayer( QString( "dbname='%1' table='%2'%3 sql=" )
-        .arg( offlineDbPath,
-              tableName, layer->hasGeometryType() ? "(Geometry)" : "" ),
+    QString connectionString = QString( "dbname='%1' table='%2'%3 sql=" )
+                               .arg( offlineDbPath,
+                                     tableName, layer->hasGeometryType() ? "(Geometry)" : "" );
+    QgsVectorLayer* newLayer = new QgsVectorLayer( connectionString,
         layer->name() + " (offline)", "spatialite" );
     if ( newLayer->isValid() )
     {
@@ -1296,33 +1301,39 @@ void QgsOfflineEditing::committedGeometriesChanges( const QString& qgisLayerId,
 void QgsOfflineEditing::startListenFeatureChanges()
 {
   QgsVectorLayer* vLayer = qobject_cast<QgsVectorLayer *>( sender() );
-  // enable logging
-  connect( vLayer->editBuffer(), SIGNAL( committedAttributesAdded( const QString&, const QList<QgsField>& ) ),
-           this, SLOT( committedAttributesAdded( const QString&, const QList<QgsField>& ) ) );
+  // enable logging, check if editBuffer is not null
+  if ( vLayer->editBuffer() )
+  {
+    connect( vLayer->editBuffer(), SIGNAL( committedAttributesAdded( const QString&, const QList<QgsField>& ) ),
+             this, SLOT( committedAttributesAdded( const QString&, const QList<QgsField>& ) ) );
+    connect( vLayer->editBuffer(), SIGNAL( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ),
+             this, SLOT( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ) );
+    connect( vLayer->editBuffer(), SIGNAL( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ),
+             this, SLOT( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ) );
+  }
   connect( vLayer, SIGNAL( committedFeaturesAdded( const QString&, const QgsFeatureList& ) ),
            this, SLOT( committedFeaturesAdded( const QString&, const QgsFeatureList& ) ) );
   connect( vLayer, SIGNAL( committedFeaturesRemoved( const QString&, const QgsFeatureIds& ) ),
            this, SLOT( committedFeaturesRemoved( const QString&, const QgsFeatureIds& ) ) );
-  connect( vLayer->editBuffer(), SIGNAL( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ),
-           this, SLOT( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ) );
-  connect( vLayer->editBuffer(), SIGNAL( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ),
-           this, SLOT( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ) );
 }
 
 void QgsOfflineEditing::stopListenFeatureChanges()
 {
   QgsVectorLayer* vLayer = qobject_cast<QgsVectorLayer *>( sender() );
-  // disable logging
-  disconnect( vLayer->editBuffer(), SIGNAL( committedAttributesAdded( const QString&, const QList<QgsField>& ) ),
-              this, SLOT( committedAttributesAdded( const QString&, const QList<QgsField>& ) ) );
+  // disable logging, check if editBuffer is not null
+  if ( vLayer->editBuffer() )
+  {
+    disconnect( vLayer->editBuffer(), SIGNAL( committedAttributesAdded( const QString&, const QList<QgsField>& ) ),
+                this, SLOT( committedAttributesAdded( const QString&, const QList<QgsField>& ) ) );
+    disconnect( vLayer->editBuffer(), SIGNAL( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ),
+                this, SLOT( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ) );
+    disconnect( vLayer->editBuffer(), SIGNAL( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ),
+                this, SLOT( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ) );
+  }
   disconnect( vLayer, SIGNAL( committedFeaturesAdded( const QString&, const QgsFeatureList& ) ),
               this, SLOT( committedFeaturesAdded( const QString&, const QgsFeatureList& ) ) );
   disconnect( vLayer, SIGNAL( committedFeaturesRemoved( const QString&, const QgsFeatureIds& ) ),
               this, SLOT( committedFeaturesRemoved( const QString&, const QgsFeatureIds& ) ) );
-  disconnect( vLayer->editBuffer(), SIGNAL( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ),
-              this, SLOT( committedAttributeValuesChanges( const QString&, const QgsChangedAttributesMap& ) ) );
-  disconnect( vLayer->editBuffer(), SIGNAL( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ),
-              this, SLOT( committedGeometriesChanges( const QString&, const QgsGeometryMap& ) ) );
 }
 
 void QgsOfflineEditing::layerAdded( QgsMapLayer* layer )