Error when trying to open empty .esp file during handle creation

[Ortham]

Reported here.

The error message is from libespm, but libloadorder shouldn't be attempting to open an empty .esm or .esp file unless it's to check if it's a valid file in the first place, and that should have exceptions caught for evaluation, rather than propagating the error.

[Ortham]

This is actually a duplicate of #12.