fix: null-guard storage targets and page tags to prevent crashes

[derekderie]

Problem

Two places in the storage layer can throw a TypeError: Cannot read properties of undefined when iterating over collections that may not be initialized:

• Storage.targets can be undefined when storage hasn't been
  activated/configured yet. Affects pageEvent, assetEvent, and
  getLocalLocations.
• currentPage.tags can be undefined when a page was imported or
  created without tags. Affects the disk storage common.js handler.

Fix

Add || [] fallback guards so these methods degrade gracefully instead of throwing:

• server/models/storage.js — 3 occurrences
• server/modules/storage/disk/common.js — 1 occurrence

[derekderie]

Found the root cause of #7978