[mutter/wip/carlosg/issue-294] backends: push missing error trap

[Carlos Garnacho <carlosg src gnome org>]

commit b3b3bf1baeca72b246fe8e0d915a9f83ce0b0a22
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri Sep 7 19:31:35 2018 +0200

    backends: push missing error trap
    
    This went MIA in commit 390314adfb6, and causes asserts when
    trying to pop a non-existent error trap a bit later.
    
    Closes: #294

 src/backends/x11/meta-input-settings-x11.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/backends/x11/meta-input-settings-x11.c b/src/backends/x11/meta-input-settings-x11.c
index 14a199e7e..d559c92a7 100644
--- a/src/backends/x11/meta-input-settings-x11.c
+++ b/src/backends/x11/meta-input-settings-x11.c
@@ -783,6 +783,9 @@ meta_input_settings_x11_set_stylus_button_map (MetaInputSettings          *setti
 
   /* Grab the puke bucket! */
   xdev = device_ensure_xdevice (device);
+
+  meta_x11_error_trap_push (display->x11_display);
+
   if (xdev)
     {
       guchar map[8] = {