Service Discovery Module: Clear cached disco info requests when detaching from stream

If a info request did not receive a response in some stream (e.g. due to network errors), any requests to the same entity in subsequent streams waited indefinitively.

xmpp-vala/src/module/xep/0030_service_discovery/module.vala

@@ -100,6 +100,8 @@ public class Module : XmppStreamModule, Iq.Handler {
     }
 
     public override void detach(XmppStream stream) {
+        active_info_requests.clear();
+
         remove_identity(stream, own_identity);
 
         stream.get_module(Iq.Module.IDENTITY).unregister_from_namespace(NS_URI_INFO, this);