fix: check if preferencesStore is defined

[piscis]

Description

This test if the preferenceStore variable is initialized. For anonymous users visiting a share link URL this is not the case and that leads to a javascript error described in #21957

By checking if the preferencesStore is defined anonymous users should not get the javascript error and chrome cast initialisation will be disabled.

Fixes #21957

How Has This Been Tested?

no tests

API Changes

none

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

none

[danieldietzler]

Thank you!