Reset attachment field after error

[meericsc]

When getting an error in adding a license attachment file, the attachment field should be cleared. Now it keeps the name of the file (that failed to upload) and allows saving the license. Reset the field in case of an error.

[Macroz]

Noticed in testing that the "save button" is enabled even before the upload has completed. This can lead to empty file in the last attachments because the requests don't finish before?