plugin XEP-0363: fixed invalid reference to slot in catched exception:

`slot` was referenced in an exception where it can't exist. This fix avoid a crash and
skip the handler when a StanzaError is catched.

sat/plugins/plugin_xep_0363.py

@@ -24,7 +24,6 @@ from urllib import parse
 from wokkel import disco, iwokkel
 from zope.interface import implementer
 from twisted.words.protocols.jabber import jid, xmlstream, error
-from twisted.words.xish import domish
 from twisted.internet import reactor
 from twisted.internet import defer
 from twisted.web import client as http_client
@@ -375,13 +374,17 @@ class XEP_0363:
             try:
                 slot = handler.callback(client, request)
             except error.StanzaError as e:
-                log.warning(f"a stanza error has been raised while processing HTTP Upload of request: {e}")
+                log.warning(
+                    "a stanza error has been raised while processing HTTP Upload of "
+                    f"request: {e}"
+                )
                 if err is None:
                     # we keep the first error to return its condition later,
                     # if no other callback handle the request
                     err = e
-            if slot:
-                break
+            else:
+                if slot:
+                    break
         else:
             log.warning(
                 _("no service can handle HTTP Upload request: {elt}")