Should exit non-zero following an exception

[captaincoordinates]

Currently validation exits with a zero exit code if an exception occurs (e.g. connection reset by peer), potentially giving the false impression of a successful validation result.

__main__.py returns here. The returned int is ignored and the script completes normally.

I suggest __main__.py should instead call sys.exit(1) as it does in the case of validation errors.

I'm happy to submit a PR if you agree that this issue is worth addressing.