tests: Workaround scan-build false positive with FD_ZERO/FD_SET

(cherry picked from commit 7aa7f8592c)

bin/tests/optional/zone_test.c

@@ -149,12 +149,11 @@ query(void) {
 	dns_fixedname_t name;
 	dns_fixedname_t found;
 	dns_db_t *db;
-	char *s;
 	isc_buffer_t buffer;
 	isc_result_t result;
 	dns_rdataset_t rdataset;
 	dns_rdataset_t sigset;
-	fd_set rfdset;
+	fd_set rfdset = { { 0 } };
 
 	db = NULL;
 	result = dns_zone_getdb(zone, &db);
@@ -169,7 +168,7 @@ query(void) {
 	dns_rdataset_init(&sigset);
 
 	do {
-
+		char *s;
 		fprintf(stdout, "zone_test ");
 		fflush(stdout);
 		FD_ZERO(&rfdset);