- Back out r304607 case 2). fgetwln() as its pair fgetln() supposed to
return partial line on any errors. See the comment in fgetln.c.
Add corresponding comment to fgetwln() too.
- Rewrite r304607 case 1).
- Remove "Fast path" from __fgetwc_mbs() since it can't detect encoding
errors and ignores them all.
PR: 212033
MFC after: 7 days