enh: free cursor if it is not a null pointer.

include/common/tmsg.h

@@ -660,8 +660,7 @@ typedef struct {
   int32_t tz;  // query client timezone
   char    intervalUnit;
   char    slidingUnit;
-  char
-      offsetUnit;  // TODO Remove it, the offset is the number of precision tickle, and it must be a immutable duration.
+  char    offsetUnit;
   int8_t  precision;
   int64_t interval;
   int64_t sliding;

source/libs/executor/src/scanoperator.c

@@ -1031,8 +1031,9 @@ static void destroySysScanOperator(void* param, int32_t numOfOutput) {
   blockDataDestroy(pInfo->pRes);
 
   const char* name = tNameGetTableName(&pInfo->name);
-  if (strncasecmp(name, TSDB_INS_TABLE_USER_TABLES, TSDB_TABLE_FNAME_LEN) == 0) {
+  if (strncasecmp(name, TSDB_INS_TABLE_USER_TABLES, TSDB_TABLE_FNAME_LEN) == 0 || pInfo->pCur != NULL) {
     metaCloseTbCursor(pInfo->pCur);
+    pInfo->pCur = NULL;
   }
 
   taosArrayDestroy(pInfo->scanCols);