Allow a full begin_random list and return to the main menu after a match

[innerhat-dev]

Summary

• A begin_random of 32 choices fits in the one word the function already uses as its mask. The check rejected that count, which stops a debug build. A shorter list is unchanged, and a longer list still fails the check.
• The map list after a match is opened with the menu history already closed. Back removed that list and left the menu world up with no buttons, logo, or music. Back on that list now leaves through the existing return to the main menu. Back on any other screen is unchanged.

Test plan

• Start a map whose begin_random has 32 choices, such as Yoyorast v2, in a debug build. The map loads.
• A begin_random with fewer than 32 choices still runs each choice once.
• Finish a network game, continue from the carnage report, then press Back on the map list. The main menu shows its buttons, logo, and music.
• Open the map list from the main menu and press Back. The screen before it returns.
• Press Back on a different screen that has no menu history. The network game stays up.