Fix the location of the fixit for -Wnewline-eof.

It turns out SourceManager treating the "one-past-the-end" location as invalid,
but then failing to set the invalid flag properly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158699 91177308-0d34-0410-b5e6-96231b3b80d8