Bugfix of "file upload limit exceeded" handling

The commons-fileupload implementation detects too large uploads already when reading the content size from the request header. The resulting exception was thrown before any uploads, on which the STATUS_ERROR_OVERSIZE could be set, were registered in the upload processor. This meant the listeners were never notified of the error.

This fix creates a dummy upload object in this case, on which the status can be set and with which the listeners can be notified.