[pgp] Adapt to Gajim MAM changes

pgp/pgpplugin.py

@@ -30,7 +30,7 @@ from gi.repository import GLib
 from gajim import dialogs
 from gajim.common import app
 from gajim.common.connection_handlers_events import (
-    MessageNotSentEvent, MessageReceivedEvent)
+    MessageNotSentEvent, MessageReceivedEvent, MamMessageReceivedEvent)
 from gajim.plugins import GajimPlugin
 
 log = logging.getLogger('gajim.plugin_system.oldpgp')
@@ -136,8 +136,10 @@ class OldPGPPlugin(GajimPlugin):
         account = conn.name
         if isinstance(obj, MessageReceivedEvent):
             enc_tag = obj.stanza.getTag('x', namespace=nbxmpp.NS_ENCRYPTED)
-        else:
+        elif isinstance(obj, MamMessageReceivedEvent):
             enc_tag = obj.msg_.getTag('x', namespace=nbxmpp.NS_ENCRYPTED)
+        else:
+            return
         if enc_tag:
             encmsg = enc_tag.getData()
             key_id = app.config.get_per('accounts', account, 'keyid')