[gtk+] x11/gl: Do not try to call MakeCurrent with a NULL context

[Emmanuele Bassi <ebassi src gnome org>]

commit 85141bc503701b5e3a25fbb5a5982da4cadeec85
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Mar 25 15:18:44 2015 +0000

    x11/gl: Do not try to call MakeCurrent with a NULL context
    
    This should not happen, but better safe than sorry.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=746746

 gdk/x11/gdkglcontext-x11.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/gdk/x11/gdkglcontext-x11.c b/gdk/x11/gdkglcontext-x11.c
index f7763e3..d9a49fd 100644
--- a/gdk/x11/gdkglcontext-x11.c
+++ b/gdk/x11/gdkglcontext-x11.c
@@ -1212,6 +1212,12 @@ gdk_x11_display_make_gl_context_current (GdkDisplay   *display,
     }
 
   context_x11 = GDK_X11_GL_CONTEXT (context);
+  if (context_x11->glx_context == NULL)
+    {
+      g_critical ("No GLX context associated to the GdkGLContext; you must "
+                  "call gdk_gl_context_realize() first.");
+      return FALSE;
+    }
 
   GDK_NOTE (OPENGL,
             g_print ("Making GLX context current to drawable %lu\n",