[muc] Only notify() about processed self-presence once
Since notify() is a rather expensive operation, we should only invoke
it once. Especially since some servers include 110 in all self
presences, not just the initially reflected one on MUC join.
[muc] Correctly processes self-presences
The change in 52a49769f9a8 ("[muc] Check for self-presence first in
presence listener") caused all self-presences (MUC user status 110) to
be ignored in the further processing chain eventually invoking
checkRoleModifications() and checkAffiliationModifications(). However,
some servers (e.g., ejabberd) include 110 not only in the initial
presence but in all following, and we ant to process these.
