Fix signature using wrong filename

There was a / missing so it would pick up userxxxx.sig rather
than user/xxxx.sig. This matches what is in write.cpp and
uedit.

exec/user_settings.js

@@ -223,7 +223,7 @@ var main_cfg = cfglib.read("main.ini");
 
 var thisuser = new User(argv[0] || user.number);
 
-const userSigFilename = system.data_dir + "user" + format("%04d.sig", thisuser.number);
+const userSigFilename = system.data_dir + "user/" + format("%04d.sig", thisuser.number);
 const PETSCII_DELETE = '\x14';
 const PETSCII_UPPERLOWER = 0x1d;