Prevent readmarker from showing until called

gajim/gtk/conversation/rows/read_marker.py

@@ -34,6 +34,7 @@ def __init__(self, account, contact):
         self.label.get_style_context().add_class(
             'conversation-read-marker')
         self.grid.attach(self.label, 0, 0, 1, 1)
+        self.set_no_show_all(True)
 
     def set_timestamp(self, timestamp):
         self.timestamp = timestamp