Fix TypeError in json_decode when template content is an array

[muhitasraf]

Summary

This PR prevents a fatal PHP TypeError in ElementorUtils::get_all_widgets_in_all_templates() when the post meta _elementor_data is retrieved as an array rather than a JSON-encoded string.

The Problem

Under certain environments, database setups, or migrations, _elementor_data post meta may be stored as a serialized PHP array in the database instead of a JSON string. When retrieved via get_post_meta($id, '_elementor_data', true), WordPress automatically unserializes it and returns a PHP array.

In PHP 8.0+, passing an array directly to json_decode() throws a fatal type error:
TypeError: json_decode(): Argument #1 ($json) must be of type string, array given

Additionally, if the metadata is corrupt or missing, passing the resulting non-array to recursively_get_inner_widgets() (which expects an array parameter) causes another fatal TypeError.

The Solution

1. Added a check is_string( $template_content ) before calling json_decode( $template_content, true ).
2. Added a check is_array( $template_content ) before merging widgets to ensure we do not pass invalid types to recursively_get_inner_widgets().
3. Skipped corrupt or empty templates cleanly via continue.