Bitmap::Crop: When the rectangle is entire bitmap, do nothing

It is expensive to rewrite the whole bitmap with the same content.

Change-Id: I001210840d535ac54837fff092c90835f9f2f547

vcl/source/gdi/bitmap.cxx

@@ -784,7 +784,7 @@ bool Bitmap::Crop( const Rectangle& rRectPixel )
 
     aRect.Intersection( Rectangle( Point(), aSizePix ) );
 
-    if( !aRect.IsEmpty() )
+    if( !aRect.IsEmpty() && aSizePix != aRect.GetSize())
     {
         BitmapReadAccess* pReadAcc = AcquireReadAccess();