Fix geometry checker relying on corrupting geometries to fix them

Geometry checker was editing geometries in place, which potentially
was corrupting other implicitly shared copies of these geometries.

src/analysis/vector/geometry_checker/qgsgeometryselfintersectioncheck.cpp

@@ -244,6 +244,7 @@ void QgsGeometrySelfIntersectionCheck::fixError( QgsGeometryCheckError *error, i
           QgsFeature newFeature;
           newFeature.setAttributes( feature.attributes() );
           newFeature.setGeometry( QgsGeometry( poly2 ) );
+          feature.setGeometry( featureGeom );
           featurePool->updateFeature( feature );
           featurePool->addFeature( newFeature );
           changes[error->layerId()][feature.id()].append( Change( ChangeRing, ChangeChanged, QgsVertexId( vidx.part, vidx.ring ) ) );
@@ -261,6 +262,7 @@ void QgsGeometrySelfIntersectionCheck::fixError( QgsGeometryCheckError *error, i
           geomCollection->removeGeometry( vidx.part );
           geomCollection->addGeometry( ringGeom1 );
           geomCollection->addGeometry( ringGeom2 );
+          feature.setGeometry( featureGeom );
           featurePool->updateFeature( feature );
           changes[error->layerId()][feature.id()].append( Change( ChangePart, ChangeRemoved, QgsVertexId( vidx.part ) ) );
           changes[error->layerId()][feature.id()].append( Change( ChangePart, ChangeAdded, QgsVertexId( geomCollection->partCount() - 2 ) ) );