'fix' #H4295 - weapon shattering

'fix' #H4295 - weapon shattering

When hero with two-handed weapon, or samurai with katana and without
shield, hits a monster which is wielding a weapon, there is a chance
for defender's weapon to be destroyed via shattering.  The chance is
reduced--by increasing the chance to resist--if the hero's weapon is
rusty or otherwise eroded.  That works as intended.  This changes
things to make the chance be increased--by reducing the chance to
resist--if defender's weapon is rusty or otherwise eroded.