PlaylistFile: convert system_error::ENOENT to PlaylistResult::NO_SUCH_LIST

src/PlaylistError.hxx

@@ -55,6 +55,11 @@ public:
 				     "No such song");
 	}
 
+	static PlaylistError NoSuchList() {
+		return PlaylistError(PlaylistResult::NO_SUCH_LIST,
+				     "No such playlist");
+	}
+
 	static PlaylistError BadRange() {
 		return PlaylistError(PlaylistResult::BAD_RANGE,
 				     "Bad song index");