Invert Mouse not working

[luther7718]

Describe the bug
"Invert Mouse" option has no effect

To Reproduce
Steps to reproduce the behavior:

1. Start game
2. Move mouse forward to look up, rearward to look down
3. Open "Options menu", check "Invert Mouse"
4. Mouse forward still makes the character look up, rearward still makes the character look down

Expected behavior
When this option is active, moving mouse forward should tilt the viewport down and vice-versa

Screenshots
N/A

Additional context
Trackball users are probably more likely to need this option