elf_begin sets elf_errno for cases that the file is completely unreadable

- The problem this is trying to solve can be seen for example thus:
	$ eu-readelf -a /
	eu-readelf: failed reading '/': (null)

  With the fix we see a proper error number and get a reasonable error
  message:

	$ eu-readelf -a /
	eu-readelf: failed reading '/': invalid file descriptor

Signed-off-by: Petr Machata <pmachata@redhat.com>
2 files changed