Fix handling of collectionChanged() in AgentBase

Since both overloads get called by Monitor, the first one would realize
the second one is implemented and instead of ignoring the change it would
call changeProcessed(). When the second overload gets called and dispatches
an actual task, when the task finished and called changeProcessed(), it
had effectively skipped a task, breaking the delicate Resource state machine

BUG: 403642
FIXED-IN: 5.11