[smuxi/stable] Frontend-GNOME: fix Gtk-CRITICAL main_loops != NULL assert on quit

[Mirco M. M. Bauer <mmmbauer src gnome org>]

commit 8b4a1a7359dc3e778a38ab454ac17edfae538701
Author: Mirco Bauer <meebey meebey net>
Date:   Mon Jan 25 18:10:58 2016 +0100

    Frontend-GNOME: fix Gtk-CRITICAL main_loops != NULL assert on quit
    
    When quitting Smuxi from the engine selection dialog, it shows a Gtk-CRITICAL
    assertion message like this:
    
        (smuxi-frontend-gnome:16423): Gtk-CRITICAL **: IA__gtk_main_quit: assertion 'main_loops != NULL' 
failed
    
    This happens because Smuxi tries to quit the GTK+ event loop without starting
    it. So check if we are in the GTK+ loop before calling Gtk.Application.Quit().

 src/Frontend-GNOME/Frontend.cs |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/src/Frontend-GNOME/Frontend.cs b/src/Frontend-GNOME/Frontend.cs
index 805d43d..e0f9d53 100644
--- a/src/Frontend-GNOME/Frontend.cs
+++ b/src/Frontend-GNOME/Frontend.cs
@@ -514,8 +514,10 @@ namespace Smuxi.Frontend.Gnome
             log4net.Core.LoggerManager.Shutdown();
 #endif
 
-            Gtk.Application.Quit();
-            
+            if (IsGtkInitialized && InGtkApplicationRun) {
+                Gtk.Application.Quit();
+            }
+
             Environment.Exit(0);
         }