…#3101)

* Fix Dispatchers.Main not being fully initialized on Android

If `unitTests.returnDefaultValues=true` is set, then
`Looper.getMainLooper()` may return `null`. The type system of
Kotlin is tricked to believe that the method can't ever return
`null`, so doesn't check for it anywhere. As a result, despite not
being fully initialized, `Dispatchers.Main` is considered
correct.

This was not an issue before, as it only surfaced when
`Dispatchers.Main` was used. However, now, `Main` is the source of
time for delays, so any delay will throw something
incomprehensible if this happens.