app crashes with FirebaseAuthWeakPasswordException Password should be at least 6 characters

current version of sign up is wrong, password is not validated on front end properly

when I enter 4 characters password, app crashes

`com.google.android.gms.tasks.RuntimeExecutionException: com.google.firebase.auth.FirebaseAuthWeakPasswordException: The given password is invalid. [ Password should be at least 6 characters ]
at com.google.android.gms.tasks.zzw.getResult(com.google.android.gms:play-services-tasks@@18.0.2:3)
at com.google.firebase.quickstart.database.kotlin.SignInFragment.signUp$lambda$5(SignInFragment.kt:102)`

The crash is reported at SignInFragment.kt:102 during signUp; inspect the password input and signup callback first. Reproduce with a four-character password, then verify invalid input is handled without the app crashing and that valid signup still works.

Written by the indexing model from the issue text.