Fix: guard $template->media reads against undefined property

[bph]

Summary

CBT_Theme_Templates::add_templates_to_local() reads $template->media in two places (templates loop, template parts loop) without checking whether the property exists. The media property is only attached by prepare_template_for_export() on code paths where there is image media to localize — on every other path, accessing it raises a PHP 8.2+ deprecation notice:

Deprecated: Creation of dynamic property … (or)
Undefined property: WP_Block_Template::$media

Change

Wrap both reads with ! empty(). This mirrors the convention used a few lines later for $template->pattern (line 238 / 266), which already uses isset().

- if ( $template->media ) {
+ if ( ! empty( $template->media ) ) {
      CBT_Theme_Media::add_media_to_local( $template->media );
  }

! empty() returns false for both undefined and falsy values, so the existing runtime behavior is preserved.

Why this is two lines, not one

There are two near-identical copies of the same loop body — one for templates, one for template parts. Both need the same guard. Worth consolidating eventually, but that is a larger refactor and not the goal here.

Test plan

• npm run lint:php clean
• npm run test:unit:php — 94 tests pass on this branch (off trunk)

No new tests added: the bug is a runtime deprecation that doesn't change observable PHPUnit outcomes on PHP 7.4 / 8.0 / 8.1, where the dynamic property assignment is still allowed without a notice. PHP 8.2+ runs in CI cover the deprecation surface.

How this was discovered

Surfaced by a strict error handler in #833's regression test. That test was narrowed to only catch the processOnlySavedTemplates notice so it would not fail on this unrelated pre-existing issue. With this PR merged, the narrowed matcher in #833 could be broadened back to the original strict handler — small follow-up, not blocking.

Closes #834

[mikachan]

Changes LGTM, thank you!

[bph]

Thank you @mikachan