We didn't properly handle the out-of-bounds case for
ConstantAggregateZero and UndefValue. This would manifest as a crash
when the constant folder was asked to fold a load of a constant global
whose struct type has no operands.
This fixes PR22595.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229352 91177308-0d34-0410-b5e6-96231b3b80d8