don't take last_status_time into account when it's a groupchat contact. Fixes #1628

src/gajim.py

@@ -776,6 +776,7 @@ class Interface:
 			# is offline, so only on Contact instance
 			if isinstance(c, list):
 				c = c[0]
+			if c: # c can be none if it's a gc contact
 				c.last_status_time = time.localtime(time.time() - array[2])
 				if array[3]:
 					c.status = array[3]