More minor bugfixes

Hey everyone!  I've finally gotten the chance to fix a few minor bugs in Gun Rounds. Here are the main ones, if you're curious about this kind of thing:

• Best time is now saved properly (before it wouldn't save unless the player already had a previous record)
• Magazine popup now displays proper symbol (ammo icon instead of gun icon)
• Contract now applies to extant enemies when player picks it up (only really relevant for the shopkeep fight)

I've submitted the update to Apple/Google, so it'll show up on those platforms whenever they approve it!