plugin XEP-0280: handle CCed messages without "to"

sat/plugins/plugin_xep_0280.py

@@ -144,7 +144,12 @@ class XEP_0280(object):
         if carbons_elt.name == "received":
             message_elt["from"] = cc_message_elt["from"]
         elif carbons_elt.name == "sent":
-            message_elt["to"] = cc_message_elt["to"]
+            try:
+                message_elt["to"] = cc_message_elt["to"]
+            except KeyError:
+                # we may not have "to" in case of message from ourself (from an other
+                # device)
+                pass
         else:
             log.warning(
                 "invalid message carbons received:\n{xml}".format(