Update src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php

Co-authored-by: Christoph Daum <c.daum@me.com>

Author: adamsilverstein

src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php

@@ -2151,7 +2151,7 @@ public function sideload_item( WP_REST_Request $request ) {
 		$size = wp_getimagesize( $path );
 
 		// Validate dimensions match expected size.
-		if ( $size ) {
+		if ( is_array( $size ) ) {
 			$validation = $this->validate_image_dimensions( $size[0], $size[1], $image_size, $attachment_id );
 			if ( is_wp_error( $validation ) ) {
 				// Clean up the uploaded file.