Testing interface fixes

A couple of fixes for the testing interface.

 * When using a translation, the name attribute for an input element would get translated as well. The resulting form element (i.e. `<input type="file" ... name="įvestis"/>`) is not recognized by the server.

 * When the contest has no tasks defined, testing interface generates (and logs) an error. While testing is quite useless in this case, i think it shouldn't fail.