Bail early if mToken.asBinder() not found

Not able to reproduce what's in the original bug report, this null check
is added as a safe guard. A possible scenario is
PipTaskOrganizer#exitPip is called twice and there is a race condition
that the first applySyncTransaction is not ready yet and leave the
internal state as it was, the second call tries to get configuration and
it is null, which leads to a NPE.

This is a counterpart of ag/12674237

Bug: 169360509
Test: N/A
Change-Id: Ife3281178f341a4118820b6e511afdab56f9ff11