security: fix missing NULL check after strdup in module-raop-discover

Memory Safety: Medium

strdup() can return NULL on allocation failure. The return value was
used without checking, which would cause a NULL pointer dereference
(crash) when the name is later compared with spa_streq(). Add a NULL
check and free the partially-allocated struct on failure.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/modules/module-raop-discover.c

@@ -147,6 +147,10 @@ static struct tunnel *tunnel_new(struct impl *impl, const char *name)
 		return NULL;
 
 	t->name = strdup(name);
+	if (t->name == NULL) {
+		free(t);
+		return NULL;
+	}
 	spa_list_append(&impl->tunnel_list, &t->link);
 
 	return t;