Only display API version if present

[TheMarex]

This only displays the version if it is specified in the info section:

Before

After

This is useful for OpenAPI specifications that bundle several APIs that are versioned independently, hence the global version string makes little sense.

[coveralls]

Coverage increased (+0.006%) to 82.209% when pulling 4b302d5 on rideOS:no_empty_version into ab943a8 on Rebilly:master.

[RomanHotsiy]

version field is required according to the OpenAPI spec:

[TheMarex]

Agreed, the implementation should conform to specs. However, it seems to me that ReDoc generally prefers to degrade in service, rather than fail if it encounters a non-compliant spec.
Given how prevalent per-operation versions are, it is questionable if the OpenAPI standard should have made this a required field in the first place, but this is a discussion for another day.

This changes simply ensures that this degradation of service is more resilient. Given how simple this change this, and that it fixes a real issue, I would advocate for merging this. If your concern is that it makes a non-compliant spec less easy to catch, I can add a warning so it remains discoverable to developers.

[RomanHotsiy]

However, it seems to me that ReDoc generally prefers to degrade in service, rather than fail if it encounters a non-compliant spec.

@TheMarex agree! Just add a warning, please.

Thanks!

[TheMarex]

@RomanGotsiy done!

[RomanHotsiy]

nice! Thanks!

[RomanHotsiy]

In the end, decided to remove the warning. ReDoc is documentation tool, not a validator :)