refactor: do some internal refactor.

source/common/src/tdatablock.c

@@ -1183,15 +1183,12 @@ static int32_t doEnsureCapacity(SColumnInfoData* pColumn, const SDataBlockInfo*
 void colInfoDataCleanup(SColumnInfoData* pColumn, uint32_t numOfRows) {
   if (IS_VAR_DATA_TYPE(pColumn->info.type)) {
     pColumn->varmeta.length = 0;
-    if (pColumn->varmeta.offset > 0) {
+    if (pColumn->varmeta.offset != NULL) {
       memset(pColumn->varmeta.offset, 0, sizeof(int32_t) * numOfRows);
     }
   } else {
     if (pColumn->nullbitmap != NULL) {
       memset(pColumn->nullbitmap, 0, BitmapLen(numOfRows));
-      if (pColumn->pData != NULL) {
-        memset(pColumn->pData, 0, pColumn->info.bytes * numOfRows);
-      }
     }
   }
 }