[gnome-shell] shell-util: ensure we've a valid n_captures when capturing images

[Jonas Ådahl <jadahl src gnome org>]

commit 4c2fd513f4c9cc208e2e6b8efd8a971082f0f99b
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Thu Jun 8 20:16:04 2017 +0800

    shell-util: ensure we've a valid n_captures when capturing images
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765011

 src/shell-util.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/shell-util.c b/src/shell-util.c
index 02db9b1..bedd586 100644
--- a/src/shell-util.c
+++ b/src/shell-util.c
@@ -461,6 +461,8 @@ shell_util_composite_capture_images (ClutterCapture  *captures,
   cairo_surface_t *image;
   cairo_t *cr;
 
+  g_assert (n_captures > 0);
+
   target_scale = 0.0;
   for (i = 0; i < n_captures; i++)
     {