Fix EZP-23739: Files uploaded with multiupload will be download with the wrong Content-Type

Files uploaded with multiupload are saved internally without suffix. This means they are downloaded as application/octet-stream which I assume is the default. Since the mimedata already contains the suffix, the patch simply adds it to the eZHTTPFile::store call, as it is done in eZBinaryFileType::fetchObjectAttributeHTTPInput() for example.
Merge pull request #1125 from glye/ezp-23739_multiupload_wrong_content_type

Fix EZP-23739: Files uploaded with multiupload will be download with the...