[mutter] backends: Fix output cycling in non display-attached tablets

[Carlos Garnacho <carlosg src gnome org>]

commit 9b9bb9cf86802a9bcbcd3b40fd9a2849e1273b02
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri Jun 16 19:21:18 2017 +0200

    backends: Fix output cycling in non display-attached tablets
    
    It would only allow to alternate between the logical monitors, we actually
    want to return NULL here so it can cycle to the whole span of monitors.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=782032

 src/backends/meta-input-settings.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/backends/meta-input-settings.c b/src/backends/meta-input-settings.c
index 96195b2..5068040 100644
--- a/src/backends/meta-input-settings.c
+++ b/src/backends/meta-input-settings.c
@@ -1637,7 +1637,7 @@ cycle_logical_monitors (MetaInputSettings   *settings,
       if (l->next)
         *next_logical_monitor = l->next->data;
       else
-        *next_logical_monitor = logical_monitors->data;
+        *next_logical_monitor = NULL;
     }
 
   return TRUE;