journal-remote: zero-initialize MHD daemon wrapper

MHDDaemonWrapper_free() unconditionally unrefs both event sources, but
setup_microhttpd_server() could return before initializing either pointer.
Zero-initialize the wrapper so cleanup after MHD startup failures safely
unrefs NULL.

Follow-up for 3c67c8bd4c

src/journal-remote/journal-remote-main.c

@@ -532,8 +532,9 @@ static int setup_microhttpd_server(RemoteServer *s,
         d = new(MHDDaemonWrapper, 1);
         if (!d)
                 return log_oom();
-
-        d->fd = (uint64_t) fd;
+        *d = (MHDDaemonWrapper) {
+                .fd = (uint64_t) fd,
+        };
 
         d->daemon = sym_MHD_start_daemon(
                         flags,