Make sure !empty() before calling String::front().

Reviewers: howard.hinnant

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D9954

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@238263 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed