command/PlaylistCommands: pass real_uri to LookupRemoteTag()

For querying tags, the real song URI should be used, because if the
(display) URI is different, requesting it will not produce a usable
response.  This is a theoretical problem because none of the existing
playlist plugins sets the real_uri.

This requires changing the URI comparison in playlist::TagModified().

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1154

src/command/PlaylistCommands.cxx

@@ -92,7 +92,7 @@ handle_load(Client &client, Request args, [[maybe_unused]] Response &r)
 	auto &instance = client.GetInstance();
 	const unsigned new_size = playlist.GetLength();
 	for (unsigned i = old_size; i < new_size; ++i)
-		instance.LookupRemoteTag(playlist.queue.Get(i).GetURI());
+		instance.LookupRemoteTag(playlist.queue.Get(i).GetRealURI());
 
 	return CommandResult::OK;
 }

src/queue/Playlist.cxx

@@ -44,13 +44,13 @@ playlist::TagModified(DetachedSong &&song) noexcept
 }
 
 void
-playlist::TagModified(const char *uri, const Tag &tag) noexcept
+playlist::TagModified(const char *real_uri, const Tag &tag) noexcept
 {
 	bool modified = false;
 
 	for (unsigned i = 0; i < queue.length; ++i) {
 		auto &song = *queue.items[i].song;
-		if (song.IsURI(uri)) {
+		if (song.IsRealURI(real_uri)) {
 			song.SetTag(tag);
 			queue.ModifyAtPosition(i);
 			modified = true;

src/queue/Playlist.hxx

@@ -196,7 +196,12 @@ public:
 	 * the song matches.
 	 */
 	void TagModified(DetachedSong &&song) noexcept;
-	void TagModified(const char *uri, const Tag &tag) noexcept;
+
+	/**
+	 * @param real_uri the song's "real uri" (see
+	 * DetachedSong::GetRealURI(), DetachedSong::IsRealURI())
+	 */
+	void TagModified(const char *real_uri, const Tag &tag) noexcept;
 
 #ifdef ENABLE_DATABASE
 	/**

src/song/DetachedSong.hxx

@@ -162,6 +162,11 @@ public:
 		return uri == other_uri;
 	}
 
+	gcc_pure gcc_nonnull_all
+	bool IsRealURI(const char *other_uri) const noexcept {
+		return (HasRealURI() ? real_uri : uri) == other_uri;
+	}
+
 	gcc_pure
 	bool IsRemote() const noexcept;