[mutter] backends/x11: Don't try to read more button states than there are

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

commit 335a85ab849c25fad4ead8fc69d207ef4abed986
Author: Sebastian Keller <skeller gnome org>
Date:   Thu Feb 11 15:42:00 2021 +0100

    backends/x11: Don't try to read more button states than there are
    
    This was causing an (inconsequential) invalid read.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1728>

 src/backends/x11/meta-seat-x11.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/backends/x11/meta-seat-x11.c b/src/backends/x11/meta-seat-x11.c
index 7ed00307f4..6ae6f5f3b5 100644
--- a/src/backends/x11/meta-seat-x11.c
+++ b/src/backends/x11/meta-seat-x11.c
@@ -1514,7 +1514,7 @@ translate_state (XIButtonState   *button_state,
 
   if (button_state)
     {
-      for (i = 1; i <= button_state->mask_len * 8; i++)
+      for (i = 1; i < button_state->mask_len * 8; i++)
         {
           if (!XIMaskIsSet (button_state->mask, i))
             continue;