e client mixer handling - fix segv where inputs/sink cause segvs
e client mixer handling - fix segv where inputs/sink cause segvs

so i've been seeing this thing where inputs are deleted and then the
sink is appropriately deleted from clients but not all the client
windows it could have been on. the problem seems to manifest if
multiple windows come from the same app playing audio so the sink may
be assigned to only 1 window not all of them.

this seems to nuke the segv as the sink/input was being left dangling on a
window due to the logic in the add/del handling to give up when it finds the
first window target and not all of them.

so after a day or so of testing my segv's are gone. yay!

@fix.

tasn/enlightenment,tasn/enlightenment,tasn/enlightenment