fixed crash when zooming out so that raster map extent is smaller than canvas pixel

git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@15760 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: rblazek

src/core/qgsrasterdataprovider.cpp

@@ -53,6 +53,9 @@ void QgsRasterDataProvider::readBlock( int bandNo, QgsRectangle  const & viewExt
 
   // TODO: init data by nulls
 
+  // If we zoom out too much, projector srcRows / srcCols maybe 0, which can cause problems in providers
+  if ( myProjector.srcRows() <= 0 || myProjector.srcCols() <= 0 ) return;
+
   // Allocate memory for not projected source data
   int mySize = dataTypeSize( bandNo ) / 8;
   void *mySrcData = malloc( mySize * myProjector.srcRows() * myProjector.srcCols() );

src/providers/grass/qgsgrassrasterprovider.cpp

@@ -211,6 +211,8 @@ void QgsGrassRasterProvider::readBlock( int bandNo, QgsRectangle  const & viewEx
   QgsDebugMsg( "pixelHeight = "  + QString::number( pixelHeight ) );
   QgsDebugMsg( "viewExtent: " + viewExtent.toString() );
 
+  if ( pixelWidth <= 0 || pixelHeight <= 0 ) return;
+
   QStringList arguments;
   arguments.append( "map=" +  mMapName + "@" + mMapset );