context: Don't forget to unref() the renderer if we create it ourselves

cogl_display_new() takes a ref on the renderer, so code creating a
renderer and not keeping a pointer to it do unref later needs to drop
the ref immediately.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit 5433555f19ac73f3f236026f1bafca758d63c9fa)

cogl/cogl-context.c

@@ -196,6 +196,7 @@ cogl_context_new (CoglDisplay *display,
         }
 
       display = cogl_display_new (renderer, NULL);
+      cogl_object_unref(renderer);
     }
   else
     cogl_object_ref (display);