Handle the case of a no-return invoke correctly. It actually still has

Handle the case of a no-return invoke correctly. It actually still has
successors, they just are all landing pad successors. We handle this the
same way as no successors. Comments attached for the next person to wade
through here and another lovely test case courtesy of Benjamin Kramer's
bugpoint reduction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145098 91177308-0d34-0410-b5e6-96231b3b80d8