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.

1 files changed, 13 insertions, 4 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 1e9f1c0848b..d6d269a700f 100644
--- a/sql/sql_select.cc
+++ b/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;