Index: src/wp-includes/class-wp-image-editor.php
===================================================================
--- src/wp-includes/class-wp-image-editor.php	(revision 42674)
+++ src/wp-includes/class-wp-image-editor.php	(working copy)
@@ -409,6 +409,7 @@
 			$fp = fopen( $filename, 'w' );
 
 			if ( ! $fp ) {
+				ob_end_clean();
 				return false;
 			}