When determining the new index for an insertelement, we may not assume that an
index greater than the size of the vector is invalid. The shuffle may be
shrinking the size of the vector. Fixes a crash!

Also drop the maximum recursion depth of the safety check for this
optimization to five.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183080 91177308-0d34-0410-b5e6-96231b3b80d8