BroadcastQueue: fix subtle resultTo bugs.

Even when no remote IApplicationThread is provided, we should still
clear out the IIntentReceiver reference so that it can be GC'ed in
the remote process.

Additionally, fix related bug where startActivityIntentSender()
has an IApplicationThread instance but doesn't pass it along.

Add log message to aid future investigations where IApplicationThread
might have been omitted by the caller.

Bug: 255833934
Test: atest --rerun-until-failure 100 NexusLauncherTests:WellbeingTests
Change-Id: I84a40c7f44eb761943e3c2aa0d3b78ffc2cbe901