shim-signed apport hook crashes under certain errors

In bug #1718582, a user has a corrupted ESP. This leads to the shim-signed apport hook crashing with the following error:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport/report.py", line 197, in _run_hook
    symb['add_info'](report, ui)
  File "/usr/share/apport/package-hooks/source_shim-signed.py", line 42, in add_info
    if directory:
UnboundLocalError: local variable 'directory' referenced before assignment

The relevant code is:

    try:
        directory = os.stat(efiboot)
    except OSError as e:
        if e.errno == errno.ENOENT:
            report['Missing'] = '/boot/efi/EFI/ubuntu directory is missing'
            return
        if e.errno == errno.EACCES:
            directory= True
    if directory:

If errno is anything other than ENOENT or EACCES, this crashes with the above traceback.

It would probably be better to at least re-raise e if it doesn't match one of our expected errnos.