[mutter] wayland/surface: Post error on invalid scale

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit f2fb3945d18de3b857ea22ae5a545e6488c112d9
Author: Robert Mader <robert mader posteo de>
Date:   Mon Mar 11 14:33:38 2019 +0100

    wayland/surface: Post error on invalid scale
    
    To follow the spec and make faulty clients fail hard.
    
    https://gitlab.freedesktop.org/wayland/wayland/blob/master/protocol/wayland.xml#L1618
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/647

 src/wayland/meta-wayland-surface.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)
---
diff --git a/src/wayland/meta-wayland-surface.c b/src/wayland/meta-wayland-surface.c
index f63d6d876..3bf9bc9ce 100644
--- a/src/wayland/meta-wayland-surface.c
+++ b/src/wayland/meta-wayland-surface.c
@@ -1072,10 +1072,17 @@ wl_surface_set_buffer_scale (struct wl_client *client,
                              int scale)
 {
   MetaWaylandSurface *surface = wl_resource_get_user_data (resource);
-  if (scale > 0)
-    surface->pending->scale = scale;
-  else
-    g_warning ("Trying to set invalid buffer_scale of %d\n", scale);
+
+  if (scale <= 0)
+    {
+      wl_resource_post_error (resource,
+                              WL_SURFACE_ERROR_INVALID_SCALE,
+                              "Trying to set invalid buffer_scale of %d\n",
+                              scale);
+      return;
+    }
+
+  surface->pending->scale = scale;
 }
 
 static void