treewide: use is_missing_file_error() where ENOENT and ENOTDIR are checked

treewide: use is_missing_file_error() where ENOENT and ENOTDIR are checked

Using the is_missing_file_error() helper introduced in the previous
step, update all hits from

  $ git grep -e ENOENT --and -e ENOTDIR

There are codepaths that only check ENOENT, and it is possible that
some of them should be checking both.  Updating them is kept out of
this step deliberately, as we do not want to change behaviour in this
step.

Signed-off-by: Junio C Hamano <gitster@pobox.com>