help to prevent current data in file from causing TDengine crashed while...

help to prevent current data in file from causing TDengine crashed while min/max function is invoked.

src/client/src/tscFunctionImpl.c

@@ -910,6 +910,16 @@ static void minMax_function(SQLFunctionCtx *pCtx, char *pOutput, int32_t isMin,
       index = pCtx->preAggVals.maxIndex;
     }
   
+    /**
+     * NOTE: work around the bug caused by invalid pre-calculated function.
+     * Here the selectivity + ts will not return correct value.
+     *
+     * The following codes of 3 lines will be removed later.
+     */
+    if (index < 0 || index >= pCtx->size + pCtx->startOffset) {
+      index = 0;
+    }
+    
     TSKEY key = pCtx->ptsList[index];
 
     if (pCtx->inputType >= TSDB_DATA_TYPE_TINYINT && pCtx->inputType <= TSDB_DATA_TYPE_BIGINT) {