[TD-98] fix a valgrind warning of accessing uninitialised value.

src/vnode/tsdb/src/tsdbMain.c

@@ -210,7 +210,7 @@ tsdb_repo_t *tsdbOpenRepo(char *tsdbDir) {
     return NULL;
   }
 
-  STsdbRepo *pRepo = (STsdbRepo *)malloc(sizeof(STsdbRepo));
+  STsdbRepo *pRepo = (STsdbRepo *)calloc(1, sizeof(STsdbRepo));
   if (pRepo == NULL) {
     return NULL;
   }