Don't raise cmdexc.CommandError in :open

:open can be called via :edit-url async, so we need to use message.error
by hand there.

qutebrowser/browser/commands.py

@@ -248,7 +248,10 @@ class CommandDispatcher:
             try:
                 url = urlutils.fuzzy_url(url)
             except urlutils.InvalidUrlError as e:
-                raise cmdexc.CommandError(e)
+                # We don't use cmdexc.CommandError here as this can be called
+                # async from edit_url
+                message.error(self._win_id, str(e))
+                return
         if tab or bg or window:
             self._open(url, tab, bg, window)
         else: