Fix edgecase crash when login fails causes crash

[MV-GH]

Fixes this crash

Atm caused by v0.19 login attempts

tried to keep error msg short, probably doesn't get fully shown atm already

java.lang.IllegalStateException: You must either set a text or a view
 at com.android.internal.util.Preconditions.checkState(Preconditions.java:215)
 at android.widget.Toast.show(Toast.java:316)
 at com.jerboa.model.LoginViewModel$login$1.invokeSuspend(Unknown Source:637)
 at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(Unknown Source:8)
 at kotlinx.coroutines.DispatchedTask.run(Unknown Source:109)
 at android.os.Handler.handleCallback(Handler.java:942)
 at android.os.Handler.dispatchMessage(Handler.java:99)
 at android.os.Looper.loopOnce(Looper.java:226)
 at android.os.Looper.loop(Looper.java:313)
 at android.app.ActivityThread.main(ActivityThread.java:8762)
 at java.lang.reflect.Method.invoke(Native Method)
 at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:604)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)

[dessalines]

Nice, thx.

BTW I've been working on the v0.19 upgrade, as we're getting ready for a backend release. ATM I've just been supporting v0.19 only, and right now I'm just thinking of upping the minimum_supported_version field. I'm not against backward compatibility, but its something I don't have time to work on, esp given the large number of API and auth-type changes to nearly every struct.