fix dirty canvas on startup

git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@13721 c8812cc2-4d05-0410-92ff-de0c093fc19c

src/gui/qgsmapcanvasmap.cpp

@@ -47,6 +47,7 @@ void QgsMapCanvasMap::resize( QSize size )
   prepareGeometryChange(); // to keep QGraphicsScene indexes up to date on size change
 
   mPixmap = QPixmap( size );
+  mPixmap.fill( mBgColor.rgb() );
   mImage = QImage( size, QImage::Format_RGB32 ); // temporary image - build it here so it is available when switching from QPixmap to QImage rendering
   mCanvas->mapRenderer()->setOutputSize( size, mPixmap.logicalDpiX() );
 }