Option to zip downloading files on the fly

So pydio can directly write the zip file to an output stream which is
connected to the user's browser without creating any temporary files.

Author: morevnaproject

core/src/core/classes/class.HTMLWriter.php

@@ -170,9 +170,11 @@ public static function generateAttachmentsHeader(&$attachmentName, $dataSize, $i
         if ($gzip) {
             header("Content-Encoding: gzip");
         }
-        header("Content-Length: ".$dataSize);
-        if ($isFile && ($dataSize != 0)) {
-            header("Content-Range: bytes 0-" . ($dataSize- 1) . "/" . $dataSize . ";");
+        if ($dataSize >= 0) {
+        	header("Content-Length: ".$dataSize);
+        	if ($isFile && ($dataSize != 0)) {
+            	header("Content-Range: bytes 0-" . ($dataSize- 1) . "/" . $dataSize . ";");
+        	}
         }
         header("Content-Disposition: attachment; filename=\"".$attachmentName."\"");
         header("Expires: 0");