Fix main menu wrapping

Due to signed/unsigned int promotion, the game would get stuck in a loop trying to display the main menu if the width of the menu entries listed was greater than the width of the terminal, e.g. when using the french translation.
Only reproduced using SDL, not sure if that just made my effective terminal narrower or if it's a SDL only issue.
FYI this is the kind of thing all those signed/unsigned warnings are supposed to catch.
Specifically, on the line ```int spacing = (window_width - menu_length) / vMenuItems.size() - 1;``` vMenuItems.size() would force the value to be unsigned, and therefore convert a negative number to a huge positive number.

While I was at it I did some coding style fixes.