Skip initial, insecure capability check if requireTLS is set

[asutherland]

In the event the server does not provide its capabilities in the greeting, browserbox will issue a CAPABILITY request even when requireTLS is going to force a STARTTLS anyways.

The control flow in _onReady and updateCapability are already non-trivial, so I figured I'd check what the preferred way to address this would be.

Note that this isn't particularly high priority since it's just a wasted roundtrip and many servers do include a CAPABILITY in their greeting, but it seems worth addressing since we would like to keep the initial connection setup as fast as possible in all cases.

[andris9]

I agree. I would like to not ask for duplicate information or for something that is not needed and BrowserBox isn't going to do anything until TLS is set up, so skipping the CAPABILITY query makes sense

[asutherland]

Thanks for the fix! I'm so very very happy we upgraded to the email.js suite of libs!