usrloc: Fix compiler warning

dlist.c: In function ‘get_all_ucontacts’:
dlist.c:750:37: error: ‘next_hop_host’ may be used uninitialized in this
			    function [-Werror=maybe-uninitialized]
      ((struct proxy_l *)cp)->name.s = next_hop_host;
                                     ^

modules/usrloc/dlist.c

@@ -495,7 +495,7 @@ cdb_pack_ping_data(const str *aor, const cdb_pair_t *contact,
 	memcpy(cp, &path.len, sizeof path.len);
 	cp += sizeof path.len;
 	memcpy(cp, path.s, path.len);
-	if (path.len > 0)
+	if (path.len != 0)
 		next_hop_host = cp + (puri.host.s - next_hop_uri.s);
 	cp += path.len;