[Merge] lp:~tiagosh/telepathy-ofono/fix-dtmf-crash into lp:telepathy-ofono

[Bill Filler]

Review: Approve

To test:
yes, just have multiple calls, send dtmf to one and switch to another, if you are unable to hangup the call then, it means tp-ofono crashed

It's all working:
Did you perform an exploratory manual test run of the code change and any related functionality on device or emulator?
yes

Did you successfully run all tests found in your component's Test Plan (https://wiki.ubuntu.com/Process/Merges/TestPlan/<package-name>) on device or emulator?
yes

Did CI run pass? If not, please explain why.
yes

Have you checked that submitter has accurately filled out the submitter checklist and has taken no shortcut?
yes

-- 
https://code.launchpad.net/~tiagosh/telepathy-ofono/fix-dtmf-crash/+merge/235055
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