t.MaxFPS 0 locks FPS to 120 instead of unlocking it in Viewport

When unlocking FPS in Viewport it defaults to 120 instead of potential max FPS. If you do this during Launch the 't.MaxFPS 0' or 't.MaxFPS -1' commands unlock the FPS to the max the GPU allows in the Viewport. When testing in Editor/PIE the commands set FPS to 120 and when in Launch the FPS was unlocked to 250+ FPS.

1. 1 Open any project in UE 4.17.2
2. 2 Go to Project Settings and uncheck 'Smooth Frame Rate'
3. 3 Enable 'Show FPS in Viewport. Take note of default FPS
4. 4 In Viewport use ` to open command line. Type in 't.MaxFPS 30'
5. 5 Type in 't.MaxFPS 500' and take note of FPS
6. 6 Type in 't.MaxFPS 0' or 't.MaxFPS -1' to unlock FPS

Results: FPS defaults back to 120 instead of being unlocked

Expected: FPS is unlocked to potential max FPS. In test case this was 250+