UDF crashes on View

When using a UDF in the WHERE clause of a view, mariadb segfaults with

mysqld[17525]: segfault at 7f533c00b180 ip 00007f533f794dff sp 00007f5328e6b720 error 4 in libgcc_s.so.1[7f533f788000+11000]

Here is a test UDF (it just returns the length of the string)

#include <string.h>
#include <mariadb/mysql.h>

//  Check arguments
my_bool testudf_init(UDF_INIT* initid,UDF_ARGS* args,char* message)
{
   if (args->arg_count!=1 || args->arg_type[0]!=STRING_RESULT)
   {
      strcpy(message,"testudf takes one string arguments");
      return 1;
   }
   initid->maybe_null=0;
   initid->const_item=0;
   return 0;
}

//  Destructor
void testudf_deinit(UDF_INIT* initid)
{
}

//  Check if IP address is with Subnet
long long testudf(UDF_INIT* initid,UDF_ARGS* args,char* is_null,char* error)
{
   //  Never returns an error or null
   *is_null = 0;
   *error = 0;
   return args->lengths[0];
}

Here is how I build and install it:

mysql devdb -e "DROP FUNCTION IF EXISTS testudf"
cp -a testudf.so /usr/lib/x86_64-linux-gnu/mariadb19/plugin
chown root:root /usr/lib/x86_64-linux-gnu/mariadb19/plugin/testudf.so
mysql devdb -e "CREATE FUNCTION testudf RETURNS integer SONAME 'testudf.so'"

Here are the tests:

CREATE TABLE x(a CHAR(8));
CREATE TABLE y(a CHAR(8));
CREATE VIEW z AS SELECT a FROM x UNION SELECT a FROM y;
INSERT INTO x VALUES('cat');
INSERT INTO y VALUES('dog');
SELECT a,testudf(a) from x;
+------+------------+
| a    | testudf(a) |
+------+------------+
| cat  |          3 |
+------+------------+
1 row in set (0.001 sec)

SELECT a,testudf(a) from y;
+------+------------+
| a    | testudf(a) |
+------+------------+
| dog  |          3 |
+------+------------+
1 row in set (0.001 sec)

SELECT a,testudf(a) from z;
+------+------------+
| a    | testudf(a) |
+------+------------+
| cat  |          3 |
| dog  |          3 |
+------+------------+
2 rows in set (0.001 sec)

SELECT a FROM x WHERE testudf(a)>2;
+------+
| a    |
+------+
| cat  |
+------+
1 row in set (0.001 sec)

SELECT a FROM y WHERE testudf(a)>2;
+------+
| a    |
+------+
| dog  |
+------+
1 row in set (0.001 sec)

SELECT a FROM z WHERE testudf(a)>2;
ERROR 2013 (HY000): Lost connection to MySQL server during query

Note that using the UDF in the WHERE clause of the view causes the segfault, but works fine everywhere else. I can't find anything in the docs that prohibits this. Is this a bug?