Sometimes I am not sure where my osu! is reading files from. This should
help somewhat.
```csharp
/Users/dean/Projects/osu/osu.Desktop/bin/Debug/net6.0/osu!
[runtime] 2022-07-13 07:22:03 [verbose]: Starting legacy IPC provider...
[runtime] 2022-07-13 07:22:03 [verbose]: Attempting to use custom storage location /Users/dean/Games/osu-lazer-2
[runtime] 2022-07-13 07:22:03 [verbose]: Storage successfully changed to /Users/dean/Games/osu-lazer-2.
[runtime] 2022-07-13 07:22:05 [verbose]: GL Initialized
```
Until now, migrating would always attempt to move files.
There's a chance that a user is reinstalling osu! but has their data at
a custom location. We want to allow the chance for them to continue
using the external data. This seems like the easiest way to make it
work.
Would be nice if we had a `Game.Restart()` method, but maybe this is
enough for now?
Note that further down the road we will probably prompt the user to
potentially select a custom install path (including one with existing
data) before osu! gets to writing anything.
They're mostly used in extensibility scenarios, so everything happens in
runtime. There is no better resolution than to crash with a null
reference exception.
`SerializationReader` is not written in a form that would support
turning nullability checking on for the entire class. The biggest
problem there is the inner `DynamicDeserializer` static class, whose
members are initialised via an `initialize()` method, which the compiler
knows nothing about.
For this reason, just opt to suppress the single inspection about
returning a `null` from a method with a return type of `string` (rider
expects `string?`). It would have been also viable to enable nullability
checking for this one method, but that's pretty much the same thing and
adds no safety anyways, so just disable the warning to minimise
surprise.
