More informative warnings

Change-Id: Idd75998f9e5e070fdaff21c6bd78c57a97007794

vcl/source/gdi/alpha.cxx

@@ -66,7 +66,8 @@ const Bitmap& AlphaMask::ImplGetBitmap() const
 
 void AlphaMask::ImplSetBitmap( const Bitmap& rBitmap )
 {
-    DBG_ASSERT( ( 8 == rBitmap.GetBitCount() ) && rBitmap.HasGreyPalette(), "AlphaMask::ImplSetBitmap: invalid bitmap" );
+    SAL_WARN_IF( 8 != rBitmap.GetBitCount(), "vcl.gdi", "Bitmap should be 8bpp, not " << rBitmap.GetBitCount() << "bpp" );
+    SAL_WARN_IF( !rBitmap.HasGreyPalette(), "vcl.gdi", "Bitmap isn't greyscale" );
     *(Bitmap*) this = rBitmap;
 }