[metacity] compositor: don't try to paint window that is not viewable

[Alberts Muktupāvels <muktupavels src gnome org>]

commit a0b8c85c4c0cfb9a378d7c5554af15fdd7703155
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sat Jun 18 18:24:00 2016 +0300

    compositor: don't try to paint window that is not viewable
    
    https://bugs.launchpad.net/ubuntu/+source/metacity/+bug/1592953

 src/compositor/compositor-xrender.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/compositor/compositor-xrender.c b/src/compositor/compositor-xrender.c
index c2ec5e7..78c3f5b 100644
--- a/src/compositor/compositor-xrender.c
+++ b/src/compositor/compositor-xrender.c
@@ -1529,6 +1529,9 @@ paint_windows (MetaScreen   *screen,
           continue;
         }
 
+      if (cw->attrs.map_state != IsViewable)
+        continue;
+
 #if 0
       if ((cw->attrs.x + cw->attrs.width < 1) ||
           (cw->attrs.y + cw->attrs.height < 1) ||