SDL_GetTicks() passes type uint

[no-lex]

The SDL function SDL_GetTicks() returns the time in ms since the library initialization, and is a uint unsigned integer; the game, however, treats the internal variable assigned to it as a signed int. This could introduce bizzare behavior if allowed to wrap around to negative numbers. This takes about 600 hours to do (596.5) to wrap around, so it would require nearly four weeks to do so. The time required to observe this behavior is likely why it has not been seen in the past.