<is_empty_asset> = true, while there is a valid, usable mediafile

[Michiel.Schok]

Seen on 1.5.7, not testen on 1.6
Related to #165 (and the basis of our experiments):

When we

1. Create an asset
2. Create an empty mediafile
3. Create an uploadticket to the mediafile
4. Create another mediafile with an URI

We have an asset with two mediafiles.
One of the mediafiles is empty (an uploadticket is issued, but never used), the other mediafile contains an URI, we observe the following when an /asset/{id} call is issued:

1. If the mediafile-id of the empty mediafile comes 'before' (alphabetically) the mediafile-id of the URI-mediafile, the <is_empty_asset> is set to TRUE
2. if it comes 'after', <is_empty_asset> is set to FALSE

This explains why roughly speaking about half our uploads of external assets goes wrong...

[forgacs]

It is ready.

[Michiel.Schok]

An error occurs at step 2 when creating the mediafile using a

[post] /mediafile/create call using parameters
user_id=foo
asset_id=y2IimNgOIYgefsTrOMEbGMyj

[robert]

ready for review for 2.1 release

[Michiel.Schok]

asset_id: W2bYcJmXJJKSUVRhrXtPyp2t
mediafile_id: m2IgsoZLFKfQlKkUNXqPV1dd (empty)
mediafile_id: S2YRIbHbZbGjY7gRKmK5bWU9 (uri)

<is_empty>false

and that is correct.