dirmngr supports the special value "none" for the key server to disable the fallback to the default key server (T6708). Kleopatra needs to handle this value in a few places to avoid confusing error messages.
Cases to be fixed:
* Search function: Using the "lookup on server" function with "none" set as keyserver causes a pop-up error window (but title is "Information") to appear which has to be recognized with OK before the results of the WKD search will be displayed. The message is "Suche auf Zertifikatsserver fehlgeschlagen. Die Fehlermeldung lautet: Kein Schlüsselserver verfügbar". (For wishes on improvements to the search dialog see T6493, too)