Fix problem with r204836

Fix problem with r204836

In CallInst, op_end() points at the callee, which we don't want to iterate over
when just iterating over arguments. Now take this into account when returning
a iterator_range from arg_operands. Similar reasoning for InvokeInst.

Also adds a unit test to verify this actually works as expected.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204851 91177308-0d34-0410-b5e6-96231b3b80d8