[PATCH][BUG_FIX] Potential null pointer dereferencing.

Hi,
ExecClearTuple don't check por NULL pointer arg and according
TupIsNull slot can be NULL.

Can anyone check this buf fix?

--- \dll\postgresql-12.0\a\backend\executor\nodeUnique.c    Mon Sep 30 17:06:55 2019
+++ nodeUnique.c    Tue Nov 12 09:54:34 2019
@@ -74,7 +74,8 @@
         if (TupIsNull(slot))
         {
             /* end of subplan, so we're done */
-            ExecClearTuple(resultTupleSlot);
+            if (!TupIsNull(resultTupleSlot))
+                ExecClearTuple(resultTupleSlot);
             return NULL;
         }