gdk: Add some return_if_fail() warnings

so we have a better chance of catching the correct cause of bugs like

https://bugzilla.gnome.org/show_bug.cgi?id=719977

diff --git a/gdk/gdkcairo.c b/gdk/gdkcairo.c
index 96243925c4b1b22570188599fca4431f94b70c4c..78003c732da895f282dfc7d27cb7db058e1e2d0b 100644 (file)
--- a/gdk/gdkcairo.c
+++ b/gdk/gdkcairo.c
@@ -284,6 +284,10 @@ gdk_cairo_surface_create_from_pixbuf (const GdkPixbuf *pixbuf,
   cairo_format_t format;
   cairo_surface_t *surface;
 
+  g_return_val_if_fail (GDK_IS_PIXBUF (pixbuf), NULL);
+  g_return_val_if_fail (scale > 0, NULL);
+  g_return_val_if_fail (for_window == NULL || GDK_IS_WINDOW (for_window), NULL);
+
   if (gdk_pixbuf_get_n_channels (pixbuf) == 3)
     format = CAIRO_FORMAT_RGB24;
   else