Fix PHP notice with null returned value from get_post_status_object()

[srtfisher]

As titled.

[GaryJones]

Thanks for the PR! You're right that get_post_status_object() can return null and we should handle that case.

Why this happens:

get_post_status_object() returns null when the status isn't registered. This can occur in several scenarios:

• Posts imported from another system with custom statuses that aren't registered in the current install
• Posts orphaned after a plugin (like Edit Flow) is deactivated, leaving posts with statuses like pitch or assigned that no longer exist
• Race conditions during plugin activation/deactivation
• Database inconsistencies

Issue with the current fix:

The current code returns early without a value:

if ( ! is_object( $post_status ) ) {
    return;
}

This effectively returns null, which breaks the display_post_states filter chain. The filter expects $post_states (an array) to be returned so other filters can continue processing. Returning null would cause issues for any subsequent filters.

Suggested fix:

if ( ! is_object( $post_status ) ) {
    return $post_states;
}

This preserves the filter chain while safely skipping our custom status display when the status object isn't available.