fs/Path: pass Path to Relative()

src/Mapper.cxx

@@ -98,7 +98,7 @@ map_fs_to_utf8(Path _path_fs)
 		if (music_dir_fs.IsNull())
 			return std::string();
 
-		path_fs = music_dir_fs.Relative(path_fs);
+		path_fs = music_dir_fs.Relative(_path_fs);
 		if (path_fs == nullptr || *path_fs == 0)
 			return std::string();
 	}

src/fs/AllocatedPath.hxx

@@ -249,8 +249,8 @@ public:
 	 * nullptr on mismatch.
 	 */
 	gcc_pure
-	const char *Relative(const char *other_fs) const {
-		return PathTraitsFS::Relative(c_str(), other_fs);
+	const_pointer Relative(Path other_fs) const {
+		return PathTraitsFS::Relative(c_str(), other_fs.c_str());
 	}
 
 	/**

src/fs/Path.hxx

@@ -153,8 +153,8 @@ public:
 	 * nullptr on mismatch.
 	 */
 	gcc_pure
-	const_pointer Relative(const_pointer other_fs) const {
-		return PathTraitsFS::Relative(value, other_fs);
+	const_pointer Relative(Path other_fs) const {
+		return PathTraitsFS::Relative(c_str(), other_fs.c_str());
 	}
 
 	gcc_pure