[PATCH] Skips PDF attachments ‘fullsize image file cannot be found’

If PDF thumbnails are not generated for any reason, you can select the attachments in the Media Library and apply Regenerate Thumbnails, but it fails with
Skipped Attachment ID nnnn (filename): The fullsize image file cannot be found in your uploads directory at . Without it, new thumbnail images can't be generated.

Looks like this was introduced in 3.1.2, as wp_get_original_image_path() returns NULL for non-image attachments. A patch to fix is:

--- wp-content/plugins/regenerate-thumbnails/includes/class-regeneratethumbnails-regenerator.php-orig	2024-06-14 21:58:34.509349816 +0100
+++ wp-content/plugins/regenerate-thumbnails/includes/class-regeneratethumbnails-regenerator.php	2024-06-15 07:05:52.566554398 +0100
@@ -138,7 +138,8 @@
 
 		if ( function_exists( 'wp_get_original_image_path' ) ) {
 			$this->fullsizepath = wp_get_original_image_path( $this->attachment->ID );
-		} else {
+		} 
+		if ( ! $this->fullsizepath ) {
 			$this->fullsizepath = get_attached_file( $this->attachment->ID );
 		}