MDEV-16235 Server crashes in my_utf8_uni or in my_strtod_int

upon SELECT .. LIMIT 0

The code must differentiate between a SELECT with contradictory
WHERE/HAVING and one with LIMIT 0.
Also for the latter printed 'Zero limit' instead of 'Impossible where'
in the EXPLAIN output.

mysql-test/r/limit.result

@@ -146,3 +146,19 @@ a
 16
 DROP TABLE t1;
 End of 5.1 tests
+#
+# mdev-16235: SELECT over a table with LIMIT 0
+#
+EXPLAIN
+SELECT * FROM mysql.slow_log WHERE sql_text != 'foo' LIMIT 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Zero limit
+SELECT * FROM mysql.slow_log WHERE sql_text != 'foo' LIMIT 0;
+start_time	user_host	query_time	lock_time	rows_sent	rows_examined	db	last_insert_id	insert_id	server_id	sql_text
+EXPLAIN
+SELECT * FROM mysql.help_topic WHERE help_category_id != example LIMIT 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Zero limit
+SELECT * FROM mysql.help_topic WHERE help_category_id != example LIMIT 0;
+help_topic_id	name	help_category_id	description	example	url
+End of 5.5 tests

mysql-test/r/subselect4.result

@@ -2512,7 +2512,7 @@ SELECT 2 IN (SELECT 2 from DUAL WHERE 1 != 1);
 SET optimizer_switch= @@global.optimizer_switch;
 set @@tmp_table_size= @@global.tmp_table_size;
 #
-# mfrv-14515: Wrong results for tableless query with subquery in WHERE
+# mdev-14515: Wrong results for tableless query with subquery in WHERE
 #             and implicit aggregation
 #
 create table t1 (i1 int, i2 int);

mysql-test/r/subselect_mat_cost_bugs.result

@@ -334,7 +334,7 @@ SELECT * FROM t1
 WHERE (f1) IN (SELECT f1 FROM t2)
 LIMIT 0;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Zero limit
 2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
 SELECT * FROM t1
 WHERE (f1) IN (SELECT f1 FROM t2)

mysql-test/t/limit.test

@@ -115,3 +115,17 @@ SELECT a FROM t1 ORDER BY a LIMIT 2 OFFSET 14;
 DROP TABLE t1;
 
 --echo End of 5.1 tests
+
+--echo #
+--echo # mdev-16235: SELECT over a table with LIMIT 0
+--echo #
+
+EXPLAIN
+SELECT * FROM mysql.slow_log WHERE sql_text != 'foo' LIMIT 0;
+SELECT * FROM mysql.slow_log WHERE sql_text != 'foo' LIMIT 0;
+
+EXPLAIN
+SELECT * FROM mysql.help_topic WHERE help_category_id != example LIMIT 0;
+SELECT * FROM mysql.help_topic WHERE help_category_id != example LIMIT 0;
+
+--echo End of 5.5 tests

mysql-test/t/subselect4.test

@@ -2047,7 +2047,7 @@ SET optimizer_switch= @@global.optimizer_switch;
 set @@tmp_table_size= @@global.tmp_table_size;
 
 --echo #
---echo # mfrv-14515: Wrong results for tableless query with subquery in WHERE
+--echo # mdev-14515: Wrong results for tableless query with subquery in WHERE
 --echo #             and implicit aggregation
 --echo #
 

sql/sql_select.cc

@@ -1136,10 +1136,19 @@ JOIN::optimize()
     if (cond_value == Item::COND_FALSE || having_value == Item::COND_FALSE || 
         (!unit->select_limit_cnt && !(select_options & OPTION_FOUND_ROWS)))
     {						/* Impossible cond */
-      DBUG_PRINT("info", (having_value == Item::COND_FALSE ? 
-                            "Impossible HAVING" : "Impossible WHERE"));
-      zero_result_cause=  having_value == Item::COND_FALSE ?
-                           "Impossible HAVING" : "Impossible WHERE";
+      if (unit->select_limit_cnt)
+      {
+        DBUG_PRINT("info", (having_value == Item::COND_FALSE ?
+                              "Impossible HAVING" : "Impossible WHERE"));
+        zero_result_cause=  having_value == Item::COND_FALSE ?
+                             "Impossible HAVING" : "Impossible WHERE";
+      }
+      else
+      {
+        DBUG_PRINT("info", ("Zero limit"));
+        zero_result_cause= "Zero limit";
+        conds= 0;
+      }
       table_count= top_join_tab_count= 0;
       error= 0;
       goto setup_subq_exit;