Make minimum bonus 0 in all cases

[AntlerForce]

The special -99 minimum value that the bonus selector gets in singleplayer would imply support for using bonus to debuff AI, but this value does not appear to do anything below 0. This PR sets this to 0 in all cases instead of multiplayer-only.

[kroIya]

Did it really not work? The handicap works in scenarios, something's not right here.

[AntlerForce]

Did it really not work? The handicap works in scenarios, something's not right here.

Negative values didn't have any visible interface change in the player list, unlike the positive bonus values which did.

[kroIya]

Negative values didn't have any visible interface change in the player list, unlike the positive bonus values which did.

I tried researching this myself a while ago but gave up, it really is unintuitive. Negative handicap worked, but it stopped showing up in the player list at some point. Instead, metal spots on the map itself will show reduced values when viewed from the handicapped team's perspective.

Mechanically, it also worked last time I checked.

I'll experiment with this again this evening to confirm, but it might warrant a revert.