[mutter] screen-cast: Fix segfault when drawing cursor

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

commit efb577efb0cd23e98caad1544f556cb82130f8e0
Author: Florian Zwoch <fzwoch gmail com>
Date:   Thu Nov 26 09:59:44 2020 +0100

    screen-cast: Fix segfault when drawing cursor
    
    Add a sanity check if the cursor is on screen and cursor texture data
    is available. This prevents a potential segfault when trying to access
    non-existing texture data.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1446
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1604>

 src/backends/meta-screen-cast-monitor-stream-src.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/backends/meta-screen-cast-monitor-stream-src.c 
b/src/backends/meta-screen-cast-monitor-stream-src.c
index 2a22dc5359..ab3be96836 100644
--- a/src/backends/meta-screen-cast-monitor-stream-src.c
+++ b/src/backends/meta-screen-cast-monitor-stream-src.c
@@ -443,6 +443,9 @@ maybe_paint_cursor_sprite (MetaScreenCastMonitorStreamSrc *monitor_src,
   cairo_surface_t *surface;
   cairo_t *cr;
 
+  if (!is_cursor_in_stream (monitor_src))
+    return;
+
   cursor_sprite = meta_cursor_renderer_get_cursor (cursor_renderer);
   if (!cursor_sprite)
     return;