INVITE command should override +b

[slingamn]

Reported by @progval in connection with #1874.

The behavior intentionally implemented in 067e62a (as per discussion recorded on #1168) was that the INVITE command should override all join restrictions, including a +b ban. However, due to a bug in 42d246b (#1171), INVITE is no longer recorded on a per-client basis unless the channel is invite-only. This functionally prevents INVITE from overriding +b unless the channel also happens to be +i. So this is officially a regression that was introduced in 2.4.0, and I need to write an irctest for it.

[yunginnanet]

YIKES

thanks for being consistent at least, I guess

[slingamn]

irctest PR: progval/irctest#125