Fix a bit sending several outgoing webcam requests + a typo fix that denies in some cases sending webcam data.

From the ReviewBoard description:

a) seems like yahoo protocol doesn't send back in the webcam
invitation accepted which person did that. and there is a variable
to remember who we sent the last invite to. Problem would be if
several invites are going to be sent. So, I made the invitation name
to be an invitation *list*. Inspired by code in libpurple.

b) there is a typo when code tries to guess who the 'accepted
invitation' is coming from. I don't have a good way to replicate,
but mostly I suspect it happens when you're sending several
invitations (see point a) ) or when some online<->offline switches
are happening. Concrete side effect is that code tries to connect
to server "".

Patch by Cristi P <cristi.posoiu AT gmail>, thanks a lot!

REVIEW: 6333