Bug #31440: 'select 1 regex null' asserts debug server

The special case with NULL as a regular expression
was handled at prepare time. But in this special case
the item was not marked as fixed. This caused an assertion
at execution time.
Fixed my marking the item as fixed even when known to 
return NULL at prepare time.

1 files changed, 1 insertions, 0 deletions

diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index 1599bcc1571..a5ede9e757c 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -4285,6 +4285,7 @@ Item_func_regex::fix_fields(THD *thd, Item **ref)
     if (args[1]->null_value)
     {						// Will always return NULL
       maybe_null=1;
+      fixed= 1;
       return FALSE;
     }
     int error;