fix: continue to fetch next row if deleted

source/dnode/vnode/src/tsdb/tsdbCache.c

@@ -1093,7 +1093,7 @@ _err:
 // iterate next row non deleted backward ts, version (from high to low)
 static int32_t nextRowIterGet(CacheNextRowIter *pIter, TSDBROW **ppRow) {
   int code = 0;
-
+  for (;;) {
     for (int i = 0; i < 4; ++i) {
       if (pIter->input[i].next && !pIter->input[i].stop) {
         code = pIter->input[i].nextRowFn(pIter->input[i].iter, &pIter->input[i].pRow);
@@ -1154,11 +1154,10 @@ static int32_t nextRowIterGet(CacheNextRowIter *pIter, TSDBROW **ppRow) {
       pIter->input[iMerge[0]].next = true;
 
       *ppRow = merge[0];
-  } else {
-    *ppRow = NULL;
+      return code;
+    }
   }
 
-  return code;
 _err:
   return code;
 }