BUG/MEDIUM: dns: don't randomly crash on out-of-memory

dns_init_resolvers() tries to emit the current resolver's name in the
error message in case of out-of-memory condition. But it must not do
it when initializing the trash before even having such a resolver
otherwise the user is certain to get a dirty crash instead of the
error message. No backport is needed.

src/dns.c

@@ -928,7 +928,7 @@ int dns_init_resolvers(void)
 
 	dns_trash_str = malloc(global.tune.bufsize);
 	if (dns_trash_str == NULL) {
-		Alert("Starting [%s] resolvers: out of memory.\n", curr_resolvers->id);
+		Alert("Starting resolvers: out of memory.\n");
 		return 0;
 	}