Prevent IllegalStateException when orphaned Fragments try to popBackStack() (EXPOSUREAPP-4430)

[d4rken]

Prevent IllegalStateException if a fragment that's not added to an Activity tries to popBackStack().

We've got a few stacktraces where the app crashes with this stacktrace (see below).

It looks like the Fragment is not added to an Activity and then we call popBackStack which throws due not not being able to find a fragment manager.

While I can't reproduce it, I think what happens is:

• User clicks "remove test"
• Then the activity is recreated, maybe because the app was put into the background, there may be other events that could get us into this state.
• When the user resumes the app the dialog is not dismissed (although it should dissmiss, and does so for me)
• The restored dialog has a reference to the previous fragment instance and calls popBackStack on that leading to the crash.

As this may be a more common error to encounter, I've added the fix (guard clause) to the extension function. "If a fragment is not added to an activity, don't popBackStack().

Originates from here:

cwa-app-android/Corona-Warn-App/src/main/java/de/rki/coronawarnapp/ui/submission/testresult/pending/SubmissionTestResultPendingFragment.kt

Line 136 in 8178542

::navigateToMainScreen

java.lang.IllegalStateException: 
  at androidx.fragment.app.Fragment.getParentFragmentManager (Fragment.java:2)
  at androidx.navigation.fragment.NavHostFragment.findNavController (NavHostFragment.java:3)
  at com.google.android.gms.common.internal.Preconditions.popBackStack
  at de.rki.coronawarnapp.ui.submission.testresult.pending.SubmissionTestResultPendingFragment.access$navigateToMainScreen (SubmissionTestResultPendingFragment.kt:1)
  at de.rki.coronawarnapp.ui.submission.testresult.pending.SubmissionTestResultPendingFragment$buildErrorDialog$1.invoke (SubmissionTestResultPendingFragment.kt:2)
  at de.rki.coronawarnapp.util.DialogHelper$showDialog$$inlined$let$lambda$1.onClick (DialogHelper.kt:3)
  at androidx.appcompat.app.AlertController$ButtonHandler.handleMessage (AlertController.java:3)
  at android.os.Handler.dispatchMessage (Handler.java:107)
  at android.os.Looper.loop (Looper.java:237)
  at android.app.ActivityThread.main (ActivityThread.java:7948)
  at java.lang.reflect.Method.invoke (Native Method)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:493)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1075)
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