Ensure Exceptions when reporting Transaction results does not cause a stall

- When TransactionManager reports onError/onTransactionCompleted, ensure that
an Exception doesn't cause the TransactionManager to stall indefinitely.
- When processTransaction throws an Exception, ensure that a stall doesn't
occur (test only verification)

Flag: EXEMPT
Test: atest TelecomUnitTests:VoipCallTransactionTest
Fixes: 315880456
Change-Id: I2db1f79e4e5d95a57945c636df9aba4b0d841aa3