Merge pull request #15144 from taosdata/fix/TS-1696-V24

fix: resolve a potential nullptr dereferencing on extraRow with update=2

src/tsdb/src/tsdbRead.c

@@ -986,7 +986,9 @@ static SMemRow getSMemRowInTableMem(STableCheckInfo* pCheckInfo, int32_t order,
       return rmem;
     } else {
       pCheckInfo->chosen = CHECKINFO_CHOSEN_BOTH;
+      if (extraRow) {
         *extraRow = rimem;
+      }
       return rmem;
     }
   } else {