[ConstantFold] Fix a crash when folding a GEP that has vector index

LLVM crashes when factoring out an out-of-bound index into preceding dimension
and the preceding dimension uses vector index.  Simply bail out now when this
case happens.

Differential Revision: https://reviews.llvm.org/D38677

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316824 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed