This is more of a safety item. To avoid potential duplicate key in
dictionary errors (and also avoid being slightly memory-leaky), allow
`SoloStatisticsWatcher` consumers to dispose of the subscriptions they
take out.
If score submission fails, the score will not receive a correct online
ID from web, but will still be passed on to the solo statistics watcher
on the results screen. This could lead to the watcher subscribing to
changes with score ID equal to the default of -1. If this happened more
than once, that would cause a crash due to duplicate keys in the
`callbacks` dictionary.
Closes#21837.
- If the local user is restricted, then attempting to fetch their data
from the `/users` endpoint would result in an empty response.
- Even if the user was successfully fetched, their `RulesetsStatistics`
may not be populated (and instead be `null`). Curiously this was not
picked up by static analysis until the first issue was fixed.
Closes#21839.
