Fix black colour defaults + license-helper PHP warning

[vapvarun]

Fixes two Bugs-column cards on woo.local (branch @ latest, v1.3.1).

Card 10251759307 - Button colour pickers default to black on fresh install

Root cause: On the Button Style tab, the four colour inputs (background, hover background, border, hover text) fell back to '' when infinite_loader_admin_button_option had no saved value. A native <input type="color"> paints #000000 on an empty value, so a fresh install rendered black pickers - and the shop Load More button - instead of the documented brand colours.

Fix: Each colour input now falls back to the same default the shop button actually renders (#1d76da background, #0e4da0 hover background, #1d76da border, #ffffff hover text - sourced from the activator seed, the public render, and the JS "Default" buttons, which all already agreed). The stale data-default="#000"/data-color="#000" on the border picker was aligned to #1d76da to match.

Seam sweep: The sibling Load Previous button tab carried the identical empty-fallback bug on the same four fields (its hover-text even fell back to #000); fixed there too.

Evidence (woo.local, option unset):

• Before: bg #000000, hover-bg #000000, border #000000, hover-text #000000
• After: bg #1d76da, hover-bg #0e4da0, border #1d76da, hover-text #ffffff

Card 10251759327 - License-helper PHP warning

Root cause: edd_infinite_loader_active_license_message() only returned an array on plugins.php / index.php / page=wbcom-license-page, returning null (and false on WP error) elsewhere. Its renderer is hooked to the shared wbcom_add_plugin_license_code action, so any other admin page that renders the section hit $license_output['message'] on null:
PHP Warning: Trying to access array offset on value of type null in edd-license/edd-plugin-license.php on line 428

Fix: The helper now always returns a well-formed array (message string + license_data object carrying a license property) on every path - off-page, WP-error, and success - so any consumer of the shared hook reads it without a warning. The EDD/SL license integration is left fully intact (no item_id/item_name changes, no EDD removal). Also collapsed the duplicated is_wp_error branch and guarded a non-object json_decode result.

Evidence (woo.local, WP_DEBUG_LOG on, rendered via the production hook on a non-license page):

• Before: line 428 null-offset warning in debug.log
• After: section renders identically (2774 bytes), zero license-helper warnings

Verification

• bash bin/build-release.sh green (version agreement, PHP lint, build-freshness, artifact file assertions) - PHP-only change, no bundle rebuild needed.
• Browser-verified per tab; saved-value path unchanged (Load Previous tab with saved colours still shows them - no regression).