src/xvba_video_glx.c: Add extra check for debugging.

src/xvba_video_glx.c

@@ -169,7 +169,7 @@ static void *render_thread(void *arg)
     /* Use the application provided display */
     Display * const x11_dpy = driver_data->x11_dpy;
 
-    ASSERT(obj_output->render_context);
+    ASSERT(obj_output->render_context == NULL);
 
     GLContextState old_cs;
     obj_output->render_context = gl_create_context(
@@ -234,6 +234,7 @@ static void *render_thread(void *arg)
 
     gl_destroy_context(obj_output->render_context);
     gl_set_current_context(&old_cs, NULL);
+
     return NULL;
 }