promise.when.then... needs a return value

[mastef]

https://github.com/SempaiGames/extension-gpgrest/blob/master/Source/com/sempaigames/gplayrest/ui/AchievementsUI.hx#L43-L46

The .then() handler after .when() is missing a return true;

See
jdonaldson/promhx#81

Otherwise triggers :
/usr/local/lib/haxe/lib/promhx/1,1,0/src/main/promhx/Promise.hx:60: characters 58-71 : Cannot use Void as value on iOS build since return is missing