BroadcastQueue: fix subtle barrier bug.

We can't immediately shortcut when mActive is past the barrier, since
there may still be pre-barrier broadcasts waiting in the other queues.

(This shortcut was only a valid optimization when we pulled mActive
from the single consistently-ordered mPending queue.)

Bug: 253906105
Test: atest FrameworksMockingServicesTests:BroadcastRecordTest
Test: atest FrameworksMockingServicesTests:BroadcastQueueTest
Test: atest FrameworksMockingServicesTests:BroadcastQueueModernImplTest
Change-Id: I6b5d37e1784a335b2992ac319d2d90c6f449c1b9