Merge branch 'develop' of http://github.com/pydio/pydio-core into develop

* 'develop' of http://github.com/pydio/pydio-core: (27 commits)
  Multiple DL: get parent base for zip file.
  Imagick: close session to avoid blocking request when generating preview. Fix resize when loading page.
  Get editable value in FormManager. Close #1124
  Fix strange display in authentication panel by passing smbclient as param instead of global_param
  Raise filtering level when downloading from remote or extarcting archive.
  Css compile
  Updated Italian translation for plugin 'core.ajaxplorer'
  Adding Italian translation for plugin 'authfront.session_login'
  Adding Italian translation for plugin 'authfront.otp'
  Adding Italian translation for plugin 'authfront.keystore'
  Adding Italian translation for plugin 'authfront.http_server'
  Adding Italian translation for plugin 'authfront.http_basic'
  Adding Italian translation for plugin 'authfront.duosecurity'
  Adding Italian translation for plugin 'authfront.cyphered'
  editor.ajxp_graphs czech translation
  editor.audio czech translation
  editor.codepress czech translation
  editor.exif czech translation
  editor.infopanel translation
  editor.soundmanager translation
  ...

Author: ghecquet

README.md

@@ -33,10 +33,10 @@ If you think you have found a bug and a way to fix it neatly in the code, use a
 
 #### Writing new plugins
 
-Please read the Developer doc located at https://pyd.io/documentation/developer, you will find here a bunch of useful information about the plugins architecture, how to create your own plugin, etc. The action.skeleton plugin is a perfect start for that. 
+Please read the Developer doc located at https://pydio.com/en/docs/developer-guide, you will find here a bunch of useful information about the plugins architecture, how to create your own plugin, etc. The action.skeleton plugin is a perfect start for that. 
 
 New in latest build, in the Settings panel, you can find a new "Developer" node where all actions contributed by all plugins are listed. These can be called either by http, or via the CLI API. At the same location, you will find all "hooks" registered and triggered in the server, that are VERY useful when you want your plugin to be really sandboxed.  
 
 #### Signing the CLA
 
-Please <a href="https://pydio.com/en/community/contribute/contributor-license-agreement-cla">sign the Contributor License Agreement</a> before contributing.
+Please [sign the Contributor License Agreement](https://pydio.com/en/community/contribute/contributor-license-agreement-cla) before contributing.

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");