[6046]<fix> fix ts always in first output index using derivative function

src/query/src/qExecutor.c

@@ -3622,7 +3622,7 @@ void updateOutputBuf(SOptrBasicInfo* pBInfo, int32_t *bufCapacity, int32_t numOf
     // re-estabilish output buffer pointer.
     int32_t functionId = pBInfo->pCtx[i].functionId;
     if (functionId == TSDB_FUNC_TOP || functionId == TSDB_FUNC_BOTTOM || functionId == TSDB_FUNC_DIFF || functionId == TSDB_FUNC_DERIVATIVE) {
-      pBInfo->pCtx[i].ptsOutputBuf = pBInfo->pCtx[i-1].pOutput;
+      if(i > 0) pBInfo->pCtx[i].ptsOutputBuf = pBInfo->pCtx[i-1].pOutput;
     }
   }
 }