Robustify SourceManager::getLocation(), so that it returns an

Robustify SourceManager::getLocation(), so that it returns an
end-of-line source location when given a column number beyond the
length of the line, or an end-of-file source location when given a
line number beyond the length of the file. Previously, we would return
an invalid location.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@97299 91177308-0d34-0410-b5e6-96231b3b80d8