Permissions controller cannot handle requests that become outdated after presentation

[shagedorn]

• present the permissions controller (the container)
• while presented, one or more "waiting" (i.e., not visible, but queued) requests becomes outdated, i.e., it cannot be presented anymore
  • this may happen when a system alert is unintentionally triggered, see Demo app requests Camera access after launch #64
  • can also happen when multiple requests (modern and legacy) are presented that share one system permission, e.g., AssetsLibrary vs Photos, AddressBook vs Contacts (currently not implemented), Local/Remote Notifications vs User Notifications

Expected result:
The stale permission is skipped silently.

Actual result:
The stale permission is skipped, but another one is presented twice, at least when opting for "Later".