<!-- You can remove this first section if you have contributed before -->
### First time contributor checklist
<!-- replace the empty checkboxes [ ] below with checked ones [x] accordingly -->
- [ ] I have read the [README](https://github.com/WhisperSystems/Signal-iOS/blob/master/README.md) and [CONTRIBUTING](https://github.com/WhisperSystems/Signal-iOS/blob/master/CONTRIBUTING.md) documents
- [ ] I have signed the [Contributor Licence Agreement](https://whispersystems.org/cla/)

### Contributor checklist
<!-- replace the empty checkboxes [ ] below with checked ones [x] accordingly -->
- [ ] I'm following the [code, UI and style conventions](https://github.com/WhisperSystems/Signal-iOS/blob/master/CONTRIBUTING.md#code-conventions)
- [ ] My commits are rebased on the latest master branch
- [ ] My commits are in nice logical chunks
- [ ] My contribution is fully baked and is ready to be merged as is
- [ ] I have tested my contribution on these devices:
 * iDevice A, iOS X.Y.Z
 * iDevice B, iOS Z.Y
- [ ] I have made the choice whether I want the [BitHub reward](https://github.com/WhisperSystems/Signal-Android/wiki/BitHub-Rewards) or not by omitting or adding the word `FREEBIE` in my commit message

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### Description
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Describe briefly what your pull request proposes to fix. Especially if you have more than one commit, it is helpful to give a summary of what your contribution as a whole is trying to solve. You can also use the `fixes #1234` syntax to refer to specific issues either here or in your commit message.
Also, please describe shortly how you tested that your fix actually works.
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