vm: Fix field default value
vm: Fix field default value

Make sure field value is initialized to zero by default.

Spotted by Valgrind.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@iki.fi>

penberg/hornet,penberg/hornet,penberg/hornet,penberg/hornet