[mutter/gnome-3-36] cogl: Defend against empty or unallocated framebuffers

[Robert Mader <rmader src gnome org>]

commit e339a57ddf87de42e8171a935a7617cd2acf7ef6
Author: Simon McVittie <smcv debian org>
Date:   Thu Apr 2 19:30:59 2020 +0100

    cogl: Defend against empty or unallocated framebuffers
    
    It isn't immediately obvious that this is impossible, because there's some
    "action at a distance" going on with framebuffers that have their size
    set lazily, after their textures get allocated; so let's make this a
    critical warning rather than crashing.
    
    In particular, this works around a crash when gnome-shell tries to blur a
    background that hasn't yet had any space allocated for it - which it seems
    is really an actor layout bug, but more robustness seems good to have.
    
    Workaround for <https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2538>.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1172
    
    Signed-off-by: Simon McVittie <smcv debian org>
    
    (cherry picked from commit c389aadff933c2d4c7fbe4f2b0864832dec40461)

 cogl/cogl/driver/gl/cogl-framebuffer-gl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/cogl/cogl/driver/gl/cogl-framebuffer-gl.c b/cogl/cogl/driver/gl/cogl-framebuffer-gl.c
index 2848d7183..e4d215ea2 100644
--- a/cogl/cogl/driver/gl/cogl-framebuffer-gl.c
+++ b/cogl/cogl/driver/gl/cogl-framebuffer-gl.c
@@ -132,8 +132,8 @@ _cogl_framebuffer_gl_flush_viewport_state (CoglFramebuffer *framebuffer)
 {
   float gl_viewport_y;
 
-  g_assert (framebuffer->viewport_width >=0 &&
-            framebuffer->viewport_height >=0);
+  g_return_if_fail (framebuffer->viewport_width >= 0);
+  g_return_if_fail (framebuffer->viewport_height >= 0);
 
   /* Convert the Cogl viewport y offset to an OpenGL viewport y offset
    * NB: OpenGL defines its window and viewport origins to be bottom