Simplify check for carbon-copied chat states

Let jlib:is_standalone_chat_state/1 unwrap carbon copies rather than
leaving this to the caller.  We still export jlib:unwrap_carbon/1, as
this function might also be useful for other purposes.

src/jlib.erl

@@ -574,14 +574,19 @@ unwrap_carbon(Stanza, Direction) ->
 
 -spec is_standalone_chat_state(xmlel()) -> boolean().
 
-is_standalone_chat_state(#xmlel{name = <<"message">>, children = Els}) ->
-    IgnoreNS = [?NS_CHATSTATES, ?NS_DELAY],
-    Stripped = [El || #xmlel{name = Name, attrs = Attrs} = El <- Els,
-		      not lists:member(fxml:get_attr_s(<<"xmlns">>, Attrs),
-				       IgnoreNS),
-		      Name /= <<"thread">>],
-    Stripped == [];
-is_standalone_chat_state(_El) -> false.
+is_standalone_chat_state(Stanza) ->
+    case unwrap_carbon(Stanza) of
+      #xmlel{name = <<"message">>, children = Els} ->
+	  IgnoreNS = [?NS_CHATSTATES, ?NS_DELAY],
+	  Stripped = [El || #xmlel{name = Name, attrs = Attrs} = El <- Els,
+			    not lists:member(fxml:get_attr_s(<<"xmlns">>,
+							     Attrs),
+					     IgnoreNS),
+			    Name /= <<"thread">>],
+	  Stripped == [];
+      #xmlel{} ->
+	  false
+    end.
 
 -spec add_delay_info(xmlel(), jid() | ljid() | binary(), erlang:timestamp())
 		     -> xmlel().

src/mod_client_state.erl

@@ -165,7 +165,7 @@ filter_presence(Acc, _Host, _Stanza) -> Acc.
 
 filter_chat_states({C2SState, _OutStanzas} = Acc, Host,
 		   #xmlel{name = <<"message">>} = Stanza) ->
-    case jlib:is_standalone_chat_state(jlib:unwrap_carbon(Stanza)) of
+    case jlib:is_standalone_chat_state(Stanza) of
       true ->
 	  From = fxml:get_tag_attr_s(<<"from">>, Stanza),
 	  To = fxml:get_tag_attr_s(<<"to">>, Stanza),

src/mod_offline.erl

@@ -455,8 +455,7 @@ need_to_store(LServer, Packet) ->
 				false ->
 				    fxml:get_subtag(Packet, <<"body">>) /= false;
 				unless_chat_state ->
-				    not jlib:is_standalone_chat_state(
-					  jlib:unwrap_carbon(Packet));
+				    not jlib:is_standalone_chat_state(Packet);
 				true ->
 				    true
 			    end