In sync_close() fix a bug introduced by the fix for Bug #59683 where we iterate

over the mutex list and free each mutex. When UNIV_MEM_DEBUG is defined, we
need skip the hash mutex.

It is a minor bug affecting only UNIV_SYNC_DEBUG builds, found by Michael.

storage/innobase/sync/sync0sync.c

@@ -1506,7 +1506,7 @@ sync_close(void)
 
 	for (mutex = UT_LIST_GET_FIRST(mutex_list);
 	     mutex != NULL;
-	     mutex = UT_LIST_GET_FIRST(mutex_list)) {
+	     /* No op */) {
 
 #ifdef UNIV_MEM_DEBUG
 		if (mutex == &mem_hash_mutex) {
@@ -1516,6 +1516,8 @@ sync_close(void)
 #endif /* UNIV_MEM_DEBUG */
 
 		mutex_free(mutex);
+
+	        mutex = UT_LIST_GET_FIRST(mutex_list);
 	}
 
 	mutex_free(&mutex_list_mutex);