resolve: initialize r during OOM

Otherwise we'd use some garbage value in the error path.

../src/resolve/resolved-dns-query.c: In function ‘dns_query_accept’:
../src/resolve/resolved-dns-query.c:944:27: error: ‘r’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  944 |         q->answer_errno = -r;
      |                           ^~
cc1: all warnings being treated as errors

Follow-up for 9ca133e97a.

src/resolve/resolved-dns-query.c

@@ -902,7 +902,7 @@ static void dns_query_accept(DnsQuery *q, DnsQueryCandidate *c) {
                         if (t->answer_ede_msg) {
                                 answer_ede_msg = strdup(t->answer_ede_msg);
                                 if (!answer_ede_msg) {
-                                        log_oom();
+                                        r = log_oom();
                                         goto fail;
                                 }
                         }