Fix possible race in user creation

[robinlinden]

This issue showed up a lot in CI where things are a lot slower. The
createprofile fragment spawns a coroutine that will create a user and
returns before it's done, then the contactlist fragment will try to load
the user, leading to a crash if the user-creation coroutine hasn't done
its thing yet.

With this change, we wait for the user-creation coroutine to complete
before moving to the contactlist fragment.

To reproduce the issue locally, I added a delay(1000) in UserManager::create.

Call stack from CI:

java.lang.IllegalStateException: The query result was empty, but expected a single row to return a NON-NULL object of type <ltd.evilcorp.core.vo.User>.
	at ltd.evilcorp.core.db.UserDao_Impl.load$lambda$3(UserDao_Impl.kt:132)
	at ltd.evilcorp.core.db.UserDao_Impl.$r8$lambda$8QDXdWcf5qEAu-VWErLGcEZTRTg(Unknown Source:0)
	at ltd.evilcorp.core.db.UserDao_Impl$$ExternalSyntheticLambda0.invoke(D8$$SyntheticClass:0)
	at androidx.room.util.DBUtil__DBUtil_androidKt$performSuspending$lambda$1$$inlined$internalPerform$1.invokeSuspend(DBUtil.kt:68)
	at androidx.room.util.DBUtil__DBUtil_androidKt$performSuspending$lambda$1$$inlined$internalPerform$1.invoke(Unknown Source:8)
	at androidx.room.util.DBUtil__DBUtil_androidKt$performSuspending$lambda$1$$inlined$internalPerform$1.invoke(Unknown Source:4)
	at androidx.room.driver.SupportSQLiteConnectionPool.useConnection(SupportSQLiteConnectionPool.android.kt:42)
	at androidx.room.RoomConnectionManager.useConnection(RoomConnectionManager.android.kt:126)
	at androidx.room.RoomDatabase.useConnection$room_runtime_release(RoomDatabase.android.kt:593)
	at androidx.room.util.DBUtil__DBUtil_androidKt$performSuspending$$inlined$compatCoroutineExecute$DBUtil__DBUtil_androidKt$1.invokeSuspend(DBUtil.android.kt:113)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:920)
	Suppressed: kotlinx.coroutines.internal.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@64390f3, Dispatchers.Main.immediate]

This has been happening on and off for a few months, but now it happened 5 times in a row in the Gradle 9 update PR and I finally decided to take the time to look into it.