Minor bug fixes

• Fixed a bug where a player who played the game a while ago would have trouble starting the game now.
• Fixed a bug where the game could save without the player object existing and create a bad save file.
• Fixed a bug with upgrades that trigger at the start of a system triggering when a game is loaded.

Also increased the Mac OS target to 10.14. Hoping this will fix things for the players who had crashes on older versions of Mac OS but I'm not 100% confident with this as I think this might be a Steamworks issue at it's root and Steam itself doesn't support versions that old.