[SM64] Fix skip act selector

[Anoliah]

The current implementation of the Skip Act Selector feature places the returns inside of lvl_set_current_level too soon. This causes a few things to not properly update when transitioning levels, most notably the coin counter. I have changed it to put the returns at the bottom of the function instead.
Also, if Skip Act Selector was not selected, then any code matching if (gCurrLevelNum == LEVEL_ENUM) return 0; in the entire level_update.c file would get deleted. This probably would never be an issue in practice, but I have updated it to only look for that pattern inside of the lvl_set_current_level function anyways.

[jesusyoshi54]

good