Support: catch invalid accesses

It is possible to invoke these methods on an invalid input resulting in an
invalid substring construction.  It seems that we do not have unit tests for
these methods.  Tests to ensure that the invalid call is caught to follow in
clang.

Resolves PR26839.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262778 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed