Reduce the clip region in ClipAndDrawGradient

We should reduce OutputDevice's clipping region to the bounds of the
polypolygon. To do this we run OutputDevice::Push(PUSH_CLIPREGION)
to have it set the clip region of the device, then intersect the clip
region of the device with the bounding rectangle.

Change-Id: I58ff5d1def1eca3c1213c7fd2d6a7205b70cdd01

vcl/source/gdi/outdev4.cxx

@@ -736,6 +736,10 @@ void OutputDevice::ClipAndDrawGradient ( Gradient &rGradient, const PolyPolygon
             if( !mpGraphics && !ImplGetGraphics() )
                 return;
 
+            // secure clip region
+            Push( PUSH_CLIPREGION );
+            IntersectClipRegion( aBoundRect );
+
             if( mbInitClipRegion )
                 ImplInitClipRegion();
 
@@ -761,6 +765,8 @@ void OutputDevice::ClipAndDrawGradient ( Gradient &rGradient, const PolyPolygon
                 else
                     ImplDrawComplexGradient( aRect, rGradient, false, &aClipPolyPoly );
             }
+
+            Pop();
         }
     }
 }