Fix: Guard block selection when iframe isn’t in Gutenberg

[andywarren]

When GiveWP’s Sequoia template runs inside an iframe on sites built with WP Bakery, the iframe isn’t wrapped in a Gutenberg .wp-block, so the block selection click handler throws. This PR adds safe checks for the frame element, .closest, and a valid data-block before dispatching block selection. That prevents errors in non-Gutenberg contexts while preserving the editor behavior when the block exists.

Affects
Sequoia template editor click handling for block selection in form.js.

Testing Instructions
Load a Sequoia form inside the block editor; click inside the form and confirm the block still selects.
Load the form on a WP Bakery page (no .wp-block ancestor) and confirm no JS errors.