No visible error message when trying to upload to a closed changeset

[Claudius]

How to reproduce:

• Upload some changes and open a new changeset and leave it open
  
• Leave JOSM open and either (a) close the changeset from another editor app or have it (b) automatically closed by the server after the open changeset timeout
  
• Do some changes in JOSM and upload again to the same changeset which still appears open to JOSM

Result:
After hitting upload button there's an error message shown for a fraction of a second and user ends up on the editing screen. In fact no upload has taken place.
When user tries to upload again it works as JOSM changed setting to opening a new changeset.

Expected result:
Error message "Changeset was closed already. Do you want to create a new instead?" which takes you back to the upload dialog.

[Gubaer]

(In [2825]) fixed #4328: No visible error message when trying to upload to a closed changeset