Simplify std::filesystem usage a little in Boot.cpp

If path_b is absolute, (path_a / path_b) will be the same as path_b.

Source/Core/Core/Boot/Boot.cpp

@@ -88,9 +88,7 @@ static std::vector<std::string> ReadM3UFile(const std::string& m3u_path,
     if (!line.empty() && line.front() != '#')  // Comments start with #
     {
 #ifdef HAS_STD_FILESYSTEM
-      const fs::path path_line = fs::u8path(line);
-      const std::string path_to_add =
-          path_line.is_relative() ? (fs::u8path(folder_path) / path_line).u8string() : line;
+      const std::string path_to_add = (fs::u8path(folder_path) / fs::u8path(line)).u8string();
 #else
       const std::string path_to_add = line.front() != '/' ? folder_path + line : line;
 #endif