fix: allow demo for older versions

We were not propagating the '--demo' flag in the legacy launcher,
unconditionally setting the 'demo' parameter to false.

Signed-off-by: flow <flowlnlnln@gmail.com>

libraries/launcher/org/polymc/applet/LegacyFrame.java

@@ -63,7 +63,8 @@ public final class LegacyFrame extends Frame {
         int winSizeH,
         boolean maximize,
         String serverAddress,
-        String serverPort
+        String serverPort,
+        boolean isDemo
     ) {
         // Implements support for launching in to multiplayer on classic servers using a mpticket
         // file generated by an external program and stored in the instance's root folder.
@@ -106,7 +107,7 @@ public final class LegacyFrame extends Frame {
         appletWrap.setParameter("sessionid", session);
         appletWrap.setParameter("stand-alone", "true"); // Show the quit button.
         appletWrap.setParameter("haspaid", "true"); // Some old versions need this for world saves to work.
-        appletWrap.setParameter("demo", "false");
+        appletWrap.setParameter("demo", isDemo ? "true" : "false");
         appletWrap.setParameter("fullscreen", "false");
 
         add(appletWrap);

libraries/launcher/org/polymc/impl/OneSixLauncher.java

@@ -137,7 +137,8 @@ public final class OneSixLauncher implements Launcher {
                         winSizeH,
                         maximize,
                         serverAddress,
-                        serverPort
+                        serverPort,
+                        mcParams.contains("--demo")
                 );
 
                 return;