Don't try to process skins in GL without a player model.

If the client receives a skin updated message from the server before having
loaded the player model (shouldn't happen, but some servers have very
strange programmers), no skin data is avaible for updating, so just bail
out.

libs/models/gl_skin.c

@@ -184,6 +184,8 @@ build_skin (skin_t *skin, int cmap)
 	s = skins + cmap;
 	if (!s->tex)
 		s = &player_skin;
+	if (!s->tex)	// we haven't loaded the player model yet
+		return;
 	texnum = skin_textures + cmap;
 	fb_texnum = 0;
 	if (s->fb)