grace_join: fix refactoring error (#6711)

Author: yumkam

ydb/library/yql/minikql/comp_nodes/mkql_grace_join_imp.cpp

@@ -462,6 +462,8 @@ void TTable::Join( TTable & t1, TTable & t2, EJoinKind joinKind, bool hasMoreLef
                 if (*slotIt != hash)
                     continue;
 
+                tuple2Idx = slotIt[slotSize - 1];
+
                 if (table1HasKeyIColumns || !(keysValSize - nullsSize1 <= slotSize - 1 - nullsSize2)) {
                     // 2nd condition cannot be true unless HasKeyStringColumns or HasKeyIColumns, hence size at the end of header is present
 
@@ -501,8 +503,6 @@ void TTable::Join( TTable & t1, TTable & t2, EJoinKind joinKind, bool hasMoreLef
                         continue;
                 }
 
-                tuple2Idx = slotIt[slotSize - 1];
-
                 tuplesFound++;
                 JoinTuplesIds joinIds;
                 joinIds.id1 = tuple1Idx;