fix: crash when showing snackbar after removing deck in widget config

[xenonnn4w]

Purpose / Description

The baseSnackbarBuilder always anchored the snackbar to the FAB, even when updateFabVisibility() had already hidden it. In debug builds this threw IllegalArgumentException ("anchorView was notvisible").

Fixes

• Fixes Crash when deleting a deck from the widget configuration screen #20301

Approach

Only anchor to the FAB when it is actually visible; otherwise fall back to default positioning.

How Has This Been Tested?

Tested by adding n number of decks( given n are maximum number of decks present) and adding all of them in the widget, then removing any one.

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner