NPE in MIME-Multipart Data Format if no file name is defined on attachment

If an MIME-Multipart message is unmarshalled into a Camel Message with attachments and the attachment parts do not have a file name defined, the MIME-Multipart data format will throw a NullPointerException (because the file name is used as the key for the map where the DataHandler is stored in the Camel Message).

The provided patch checks whether there is a file name defined on the data handler. If this is not the case the Content-ID header of the attachment is used, if that is also not defined a unique id is generated for the key.

See the two attached MIME-Multipart documents used in the unit tests for details.