Fixed issue related with committing previously aborted key during re-keying

This doesn't have any security implications (albeit it potentially could, thanks to [this line](https://github.com/DrKLO/Telegram/blob/8c50d4d03bdda3839978e55ae1f0a2ca5492b0f6/TMessagesProj/src/main/java/org/telegram/android/SecretChatHelper.java#L840)), but it will consistently break the secret chat in the case of not matching fingerprints during re-keying.