fix #H6292 - green slime & genocide

fix #H6292 - green slime & genocide

Report suggested that if hero is turning into green slime, genociding
green slime should cure it.  I went another direction:  if life-saved
while dying due to turning into green slime, you survive polymorphed
into green slime form.  If green slimes have been genocided (probably
after becoming infected with slime or hero wouldn't have faced any
slimes to cause infection, but that could be from eating a glob of
green slime created prior to genocide, or from #wizintrinsic), you'll
immediately die again, this time from genocide.