MDEV-33987 Server crashes at Item_func_as_wkt::val_str_ascii

Item_func_boundary::val_str() did not set null_value when
it could not construct a geomery object from the input.

Author: abarkov

mysql-test/main/gis.result

@@ -5453,4 +5453,10 @@ t2	CREATE TABLE `t2` (
   `c` polygon DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
 drop table t1, t2;
+#
+# MDEV-33987 Server crashes at Item_func_as_wkt::val_str_ascii
+#
+SELECT ST_ASTEXT(BOUNDARY(INET6_ATON('255.255.255.255'))) AS c1;
+c1
+NULL
 # End of 10.5 tests

mysql-test/main/gis.test

@@ -3456,4 +3456,12 @@ create table t2 as select group_concat(c, c order by 1,2), concat(c), c from t1;
 show create table t2;
 drop table t1, t2;
 
+
+--echo #
+--echo # MDEV-33987 Server crashes at Item_func_as_wkt::val_str_ascii
+--echo #
+
+SELECT ST_ASTEXT(BOUNDARY(INET6_ATON('255.255.255.255'))) AS c1;
+
+
 --echo # End of 10.5 tests

sql/item_geofunc.cc

@@ -452,7 +452,7 @@ String *Item_func_boundary::val_str(String *str_value)
   Transporter trn(&res_receiver);
 
   Geometry *g= Geometry::construct(&buffer, swkb->ptr(), swkb->length());
-  if (!g)
+  if ((null_value= !g))
     DBUG_RETURN(0);
 
   if (g->store_shapes(&trn))