MDEV-621: LP:693329 - Assertion `!is_interleave_error' failed on low optimizer_search_depth

- When restore_prev_nj_state() is called for the table that is 
  the last remaining child of a nested join, do not leave that
  nested join's bit in join->cur_embedding_map.

mysql-test/r/join_nested.result

@@ -1847,3 +1847,27 @@ Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t2`.`a` AS `a`,`test`.`t3`.`a` A
 DROP TABLE t1,t2,t3,t4;
 SET optimizer_switch=@save_optimizer_switch;
 End of 5.0 tests
+#
+# MDEV-621: LP:693329 - Assertion `!is_interleave_error' failed on low optimizer_search_depth
+#
+set @tmp_mdev621= @@optimizer_search_depth;
+SET SESSION optimizer_search_depth = 4;
+CREATE TABLE t1 (f1 int,f2 int,f3 int,f4 int) ;
+INSERT IGNORE INTO t1 VALUES (0,0,2,0),(NULL,0,2,0);
+CREATE TABLE t2 (f1 int) ;
+CREATE TABLE t3 (f3 int,PRIMARY KEY (f3)) ;
+CREATE TABLE t4 (f5 int) ;
+CREATE TABLE t5 (f2 int) ;
+SELECT alias2.f4  FROM t1  AS alias1
+LEFT    JOIN t1  AS alias2
+LEFT  JOIN t2  AS alias3
+LEFT  JOIN t3  AS alias4  ON alias3.f1 = alias4.f3
+ON alias2.f1
+LEFT    JOIN t4  AS alias5
+JOIN t5  ON alias5.f5
+ON alias2.f3  ON alias1.f2;
+f4
+NULL
+NULL
+DROP TABLE t1,t2,t3,t4,t5;
+set optimizer_search_depth= @tmp_mdev621;

mysql-test/t/join_nested.test

@@ -1287,3 +1287,27 @@ SET optimizer_switch=@save_optimizer_switch;
 
 --echo End of 5.0 tests
 
+--echo #
+--echo # MDEV-621: LP:693329 - Assertion `!is_interleave_error' failed on low optimizer_search_depth
+--echo #
+set @tmp_mdev621= @@optimizer_search_depth;
+SET SESSION optimizer_search_depth = 4;
+
+CREATE TABLE t1 (f1 int,f2 int,f3 int,f4 int) ;
+INSERT IGNORE INTO t1 VALUES (0,0,2,0),(NULL,0,2,0);
+CREATE TABLE t2 (f1 int) ;
+CREATE TABLE t3 (f3 int,PRIMARY KEY (f3)) ;
+CREATE TABLE t4 (f5 int) ;
+CREATE TABLE t5 (f2 int) ;
+
+SELECT alias2.f4  FROM t1  AS alias1
+LEFT    JOIN t1  AS alias2
+        LEFT  JOIN t2  AS alias3
+        LEFT  JOIN t3  AS alias4  ON alias3.f1 = alias4.f3
+        ON alias2.f1
+LEFT    JOIN t4  AS alias5
+        JOIN t5  ON alias5.f5
+ON alias2.f3  ON alias1.f2;
+DROP TABLE t1,t2,t3,t4,t5;
+set optimizer_search_depth= @tmp_mdev621;
+

sql/sql_select.cc

@@ -13262,13 +13262,13 @@ static void restore_prev_nj_state(JOIN_TAB *last)
       
       bool was_fully_covered= nest->is_fully_covered();
       
+      join->cur_embedding_map|= nest->nj_map;
+
       if (--nest->counter == 0)
         join->cur_embedding_map&= ~nest->nj_map;
       
       if (!was_fully_covered)
         break;
-      
-      join->cur_embedding_map|= nest->nj_map;
     }
   }
 }