[nq,qw] Call Mod_ClearAll in CL_Shutdown

Although the model subsystem does this too, it does it too late relative
to the video shutdown, resulting in segfaults for glsl due to the
drivers having been unloaded.

libs/models/model.c

@@ -161,6 +161,7 @@ mod_unload_model (size_t ind)
 	//with alias models
 	if (!mod->needload && mod->clear) {
 		mod->clear (mod, mod->data);
+		mod->clear = 0;
 	}
 	if (mod->type != mod_alias) {
 		mod->needload = true;

nq/source/cl_main.c

@@ -216,6 +216,8 @@ static void
 CL_Shutdown (void *data)
 {
 	CL_WriteConfiguration ();
+
+	Mod_ClearAll ();
 }
 
 void

qw/source/cl_main.c

@@ -1440,6 +1440,8 @@ CL_Shutdown (void *data)
 	dstring_delete (cls.downloadname);
 	dstring_delete (cls.downloadurl);
 	free (cl.players);
+
+	Mod_ClearAll ();
 }
 
 void