fs/StandardDirectory: use mode=0777 in mkdir() call

Of course, mode=0700 is more secure, but allowing other users access
to new directories is a choice the user should make via umask().  If
the user-chosen umask allows everybody access, MPD should probably
respect that.

src/fs/StandardDirectory.cxx

@@ -308,7 +308,7 @@ GetAppRuntimeDir() noexcept
 #ifdef USE_XDG
 	if (const auto user_dir = GetUserRuntimeDir(); !user_dir.IsNull()) {
 		auto dir = user_dir / Path::FromFS("mpd");
-		mkdir(dir.c_str(), 0700);
+		mkdir(dir.c_str(), 0777);
 		return dir;
 	}
 #endif