[td-225]add check for malloc failure.

src/tsdb/src/tsdbRead.c

@@ -477,6 +477,10 @@ static STsdbQueryHandle* tsdbQueryTablesImpl(STsdbRepo* tsdb, STsdbQueryCond* pC
 
 TsdbQueryHandleT* tsdbQueryTables(STsdbRepo* tsdb, STsdbQueryCond* pCond, STableGroupInfo* groupList, uint64_t qId, SMemRef* pRef) {
   STsdbQueryHandle* pQueryHandle = tsdbQueryTablesImpl(tsdb, pCond, qId, pRef);
+  if (pQueryHandle == NULL) {
+    return NULL;
+  }
+
   if (emptyQueryTimewindow(pQueryHandle)) {
     return (TsdbQueryHandleT*) pQueryHandle;
   }
@@ -587,6 +591,10 @@ TsdbQueryHandleT tsdbQueryLastRow(STsdbRepo *tsdb, STsdbQueryCond *pCond, STable
   }
 
   STsdbQueryHandle *pQueryHandle = (STsdbQueryHandle*) tsdbQueryTables(tsdb, pCond, groupList, qId, pMemRef);
+  if (pQueryHandle == NULL) {
+    return NULL;
+  }
+
   int32_t code = checkForCachedLastRow(pQueryHandle, groupList);
   if (code != TSDB_CODE_SUCCESS) { // set the numOfTables to be 0
     terrno = code;
@@ -604,6 +612,10 @@ TsdbQueryHandleT tsdbQueryLastRow(STsdbRepo *tsdb, STsdbQueryCond *pCond, STable
 
 TsdbQueryHandleT tsdbQueryCacheLast(STsdbRepo *tsdb, STsdbQueryCond *pCond, STableGroupInfo *groupList, uint64_t qId, SMemRef* pMemRef) {
   STsdbQueryHandle *pQueryHandle = (STsdbQueryHandle*) tsdbQueryTables(tsdb, pCond, groupList, qId, pMemRef);
+  if (pQueryHandle == NULL) {
+    return NULL;
+  }
+
   int32_t code = checkForCachedLast(pQueryHandle);
   if (code != TSDB_CODE_SUCCESS) { // set the numOfTables to be 0
     terrno = code;