Google Docs files are not synced in the client cause server reports empty content lenght

[SamuAlfageme]

As "Google Docs files are free", they are causing an error in the desktop client when syncing since their exported versions do have size.

Steps to reproduce

1. Create files with Google Drive interface (Docs, Spreadsheets, Presentations, ...)
2. Configure Google Drive as External Storage option
3. Sync with the desktop client

Expected behaviour

The files can be synced by the client and are the same that can be downloaded via the web interface (the results of the export with GDrive)

Actual behaviour

The files are included in the Not Synced tab with the action: Broken webserver returning empty content length for non-empty file on resume and therefore, ignored.

Server configuration

• Operating system: CentOS 6.6
• Web server: Apache
• Database: MySQL
• PHP version: 7.0
• ownCloud version: 9.1.3 RC1

@PVince81