Bell should be immediately cancelled when user tries to "cancel" it

[jpassaro]

Setup:

• Bell rings.
• While playback is still ongoing (e.g. within one second of the bell ring), user presses cancel button or locks phone.

Expected:

• Bell sound ceases immediately

Actual behavior:

• Bell sound continues.

Is it possible to support cutting off the bell sound this way, e.g. if user is in a meeting?

Happy to contribute and test a patch if somebody can point me at the right section of code.