fix: skip update logs for items whose identifier was cleared on removal

[paullla]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Issues	-
License	MIT

Problem

Deleting a parent entity together with its LoggableChildInterface children crashes the update handler. The child's delete log triggers an update log for the parent (ActivityLogger::handleLoggableChild()), but by then Doctrine has already cleared the parent's generated identifier. The current data tracker lookup then runs a term query with objectId: null, which Elasticsearch rejects with 400 illegal_argument_exception: field name is null or empty, failing the whole flush flow.

Found while driving a real application (demo app with Product -> ProductVariant as loggable child) against 2.0-dev.

Changes

• UpdateActivityLogHandler returns early when the updated item's identifier is null: an item without an identifier has no current data tracker to compare against, its own delete log is already written, and an edit log for a removed entity is meaningless
• Unit test asserting the tracker provider and processor are never called for an identifier-less item

Verification

• Reproduced in the demo app: delete of a product with variants failed with the 400 before the fix and completes after it, with the expected Created/Edited/Deleted logs intact
• Full PHPUnit suite (25 tests, 55 assertions) green against Elasticsearch 9.0; PHPStan clean; PHP-CS-Fixer clean