[gnome-flashback] display-config: don't set underscan property when not supported

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 9a4f895d27bf0452f45fab5d5343d36c1abad18a
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Wed Jul 1 17:59:36 2015 -0700

    display-config: don't set underscan property when not supported
    
    We should not be setting random output properties like this.
    Use the function we just introduced to only set the underscan flag when
    it's actually supported.
    
    Mutter commit:
    https://git.gnome.org/browse/mutter/commit/?id=659b8ed471b49b583e8bc30d99bbdb6bb8d44c3e

 .../libdisplay-config/flashback-monitor-manager.c  |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/gnome-flashback/libdisplay-config/flashback-monitor-manager.c 
b/gnome-flashback/libdisplay-config/flashback-monitor-manager.c
index 572be4c..bc62c60 100644
--- a/gnome-flashback/libdisplay-config/flashback-monitor-manager.c
+++ b/gnome-flashback/libdisplay-config/flashback-monitor-manager.c
@@ -1790,9 +1790,10 @@ flashback_monitor_manager_apply_configuration (FlashbackMonitorManager  *manager
                                       output_info->output,
                                       output_info->is_presentation);
 
-      output_set_underscanning_xrandr (priv,
-                                       output_info->output,
-                                       output_info->is_underscanning);
+      if (output_get_supports_underscanning_xrandr (priv, output_info->output))
+        output_set_underscanning_xrandr (priv,
+                                         output_info->output,
+                                         output_info->is_underscanning);
 
       output->is_primary = output_info->is_primary;
       output->is_presentation = output_info->is_presentation;