[Support] Don't return an error if realPath fails.
In openFileForRead, we would not previously return an error
if real_path resolution failed. After a recent patch, we
started propagating this error up. This caused a failure
in clang when trying to call openFileForRead("nul"). This
patch restores the previous behavior of not propagating this
error up.
llvm-svn: 297488
GitOrigin-RevId: 3c0dc3360075de6bcdd2de9b19ca0879ebb6980d