fix the conditions for achievement progress indication

[otavepto]

• fix the conditions for progress indication
• remove invalid code when resetting stats
• don't reset achievement max_progress, this is defined in the schema, the running value is progress

fixes for both, the user achievements.json in the saves folder + the overlay tested on appid 1583230

I acknowledge this introduces a new warning (conversion from float to uint32) and I left it intentionally so we don't forget about it later. The original function Steam_User_Stats::IndicateAchievementProgress() works only with uint32, but it looks like some stats could be float, since there's no overload, I was lazy and didn't bother adding one :/

[otavepto]

I pushed more commits to complete/finalize this:

• remove invalid condition when resetting stats, only write to disk and share stats with gameserver if value isn't already the default
• try-catch access to progress and max_progress during construction since they throw exception for achievements with no progress, making them standalone/safe
• always trigger UserStatsStored_t and UserAchievementStored_t callbacks in Steam_User_Stats::IndicateAchievementProgress() even if value wasn't updated, games my halt otherwise
• return false in Steam_User_Stats::GetAchievementProgressLimits() if the achievement has no progress