Mentions with /myroomnick are not translated correctly to IRC

[zouppen]

Describe the bug
When a native Matrix user mentions someone who has set /myroomnick on that channel, it is not being converted to IRC nickname on IRC. This makes following the conversation difficult on IRC.

To Reproduce
Steps to reproduce the behavior:

1. Matrix user Alice runs /myroomnick Alpha
2. Matrix user Bob mentions the nick name Alpha using the pill (writing for example Alp<tab>)
3. IRC user Igor sees <Bob> Alpha: message content

Expected behavior
IRC user Igor should see <Bob> Alice: message content because Alice is her nickname on IRC. IRC doesn't support myroomnick, so it should show the real IRC nick instead, like /myroomnick was never run.

Screenshots

13:41 <@Bob> Alpha: message content
13:43 <@Alice> Bob: another message