[mutter] renderer/native: Prepare for real page flips without primary plane changes

[Marge Bot <marge-bot src gnome org>]

commit dd03ffa89d2750675b3b9e6730872c84ee96853b
Author: Jonas Ådahl <jadahl gmail com>
Date:   Sat Oct 10 01:22:54 2020 +0200

    renderer/native: Prepare for real page flips without primary plane changes
    
    This is something that the atomic backend will need, as cursor updates
    go through page flips too.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1488>

 src/backends/native/meta-renderer-native.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index f1b9c749b9..8e204a6e4f 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -1010,6 +1010,9 @@ meta_onscreen_native_swap_drm_fb (CoglOnscreen *onscreen)
   CoglOnscreenEGL *onscreen_egl =  onscreen->winsys;
   MetaOnscreenNative *onscreen_native = onscreen_egl->platform;
 
+  if (!onscreen_native->gbm.next_fb)
+    return;
+
   free_current_bo (onscreen);
 
   g_set_object (&onscreen_native->gbm.current_fb, onscreen_native->gbm.next_fb);