Fix some clazy container-inside-loop warnings

From the clazy docs:

"Finds places defining containers inside loops. Defining them
outside the loop and using resize(0) will save memory allocations."

Author: nyalldawson

src/core/qgsogcutils.cpp

@@ -653,9 +653,10 @@ QgsGeometry QgsOgcUtils::geometryFromGMLMultiPolygon( const QDomElement& geometr
   QDomNodeList currentPosList;
 
   QDomNodeList polygonMemberList = geometryElement.elementsByTagNameNS( GML_NAMESPACE, "polygonMember" );
+  QgsPolygon currentPolygonList;
   for ( int i = 0; i < polygonMemberList.size(); ++i )
   {
-    QgsPolygon currentPolygonList;
+    currentPolygonList.resize( 0 ); // preserve capacity - don't use clear
     currentPolygonMemberElement = polygonMemberList.at( i ).toElement();
     polygonList = currentPolygonMemberElement.elementsByTagNameNS( GML_NAMESPACE, "Polygon" );
     if ( polygonList.size() < 1 )

src/core/symbology-ng/qgsinvertedpolygonrenderer.cpp

@@ -259,8 +259,12 @@ void QgsInvertedPolygonRenderer::stopRender( QgsRenderContext& context )
     return;
   }
 
+  QgsMultiPolygon finalMulti; //avoid expensive allocation for list for every feature
+  QgsPolygon newPoly;
+
   Q_FOREACH ( const CombinedFeature& cit, mFeaturesCategories )
   {
+    finalMulti.resize( 0 ); //preserve capacity - don't use clear!
     QgsFeature feat = cit.feature; // just a copy, so that we do not accumulate geometries again
     if ( mPreprocessingEnabled )
     {
@@ -283,7 +287,7 @@ void QgsInvertedPolygonRenderer::stopRender( QgsRenderContext& context )
       //
       // No validity check is done, on purpose, it will be very slow and painting
       // operations do not need geometries to be valid
-      QgsMultiPolygon finalMulti;
+
       finalMulti.append( mExtentPolygon );
       Q_FOREACH ( const QgsGeometry& geom, cit.geometries )
       {
@@ -312,9 +316,9 @@ void QgsInvertedPolygonRenderer::stopRender( QgsRenderContext& context )
           // add interior rings as new polygons
           for ( int j = 1; j < multi[i].size(); j++ )
           {
-            QgsPolygon new_poly;
-            new_poly.append( multi[i][j] );
-            finalMulti.append( new_poly );
+            newPoly.resize( 0 ); //preserve capacity - don't use clear!
+            newPoly.append( multi[i][j] );
+            finalMulti.append( newPoly );
           }
         }
       }