fix: room chat - whisper displays 1 mention when 2 mentions are send in specific way

[NJ-2020]

Fixed Issues

$ Expensify/App#46299

Tests

1. What unit/integration tests cover your change? What autoQA tests cover your change?
2. What tests did you perform that validates your changed worked?
3. Go to Expensify App
4. Tap on a room chat
5. Mention 2 user with minus sign in between i.e #user1-#user2
6. Verify that whisper display 2 user

QA

1. What does QA need to do to validate your changes?
2. What areas to they need to test for regressions?
3. Same as Tests

[rojiphil]

@NJ-2020 Can you please fill in the PR Author Checklist and follow the contributing guidelines as mentioned here and here.
The PR Author Checklist must be the contents of the PR description.