BACKPORT: udf: Check path length when reading symlink

Symlink reading code does not check whether the resulting path fits into
the page provided by the generic code. This isn't as easy as just
checking the symlink size because of various encoding conversions we
perform on path. So we have to check whether there is still enough space
in the buffer on the fly.

Upstream commit: 0e5cc9a4
CC: stable@vger.kernel.org
Reported-by: Carl Henrik Lunde <chlunde@ping.uio.no>
Bug: 35841292
Signed-off-by: Jan Kara <jack@suse.cz>
Change-Id: I91c49f41c9bb9f5c6898bbcd5f125f3accb70a57