Fix PHP Notice: ob_end_clean(): failed to delete buffer.

main/inc/lib/document.lib.php

@@ -327,7 +327,7 @@ class DocumentManager
             header('Content-Description: '.$filename);
             header('Content-Transfer-Encoding: binary');
 
-            if (function_exists('ob_end_clean')) {
+            if (function_exists('ob_end_clean') && ob_get_length()) {
                 // Use ob_end_clean() to avoid weird buffering situations
                 // where file is sent broken/incomplete for download
                 ob_end_clean();
@@ -393,7 +393,7 @@ class DocumentManager
                 );
                 echo $content;
             } else {
-                if (function_exists('ob_end_clean')) {
+                if (function_exists('ob_end_clean') && ob_get_length()) {
                     // Use ob_end_clean() to avoid weird buffering situations
                     // where file is sent broken/incomplete for download
                     ob_end_clean();