patrol: Wait for feed to finish before waking up MassPatrol
patrol: Wait for feed to finish before waking up MassPatrol

Previously if the user already has an active feed and then creates
a user filter and enables MassPatrol int he same update (e.g. not
pressing "Apply" in between before enabling MassPatrol) then
MassPatrol would start by opening the first diff in the existing
feed where the user filter had not been applied yet (which could
be unrelated).

Krinkle/mw-gadget-rtrc