Make thread requirements of ReplayHandler#setup explicit and fix illegal usage

src/main/java/com/replaymod/replay/FullReplaySender.java

@@ -845,11 +845,11 @@ public class FullReplaySender extends ChannelDuplexHandler implements ReplaySend
                         startFromBeginning = false;
                         nextPacket = null;
                         lastPacketSent = System.currentTimeMillis();
-                        replayHandler.restartedReplay();
                         if (replayIn != null) {
                             replayIn.close();
                             replayIn = null;
                         }
+                        ReplayMod.instance.runSync(replayHandler::restartedReplay);
                     }
                 }
             } catch (Exception e) {

src/main/java/com/replaymod/replay/ReplayHandler.java

@@ -161,25 +161,22 @@ public class ReplayHandler {
     }
 
     void restartedReplay() {
+        Preconditions.checkState(isOnMainThread(), "Must be called from Minecraft thread.");
+
         channel.close();
 
-        // Force re-creation of camera entity by unloading the previous world
-        try {
-            ReplayMod.instance.runSync(() -> {
         //#if MC>=11300
         mc.mouse.unlockCursor();
         //#else
         //$$ mc.setIngameNotInFocus();
         //#endif
+
+        // Force re-creation of camera entity by unloading the previous world
         //#if MC>=11400
         mc.disconnect();
         //#else
         //$$ mc.loadWorld(null);
         //#endif
-            });
-        } catch (InterruptedException | ExecutionException | TimeoutException e) {
-            LOGGER.error("Failed to properly restart (shutdown) replay:", e);
-        }
 
         restrictions = new Restrictions();
 
@@ -236,6 +233,8 @@ public class ReplayHandler {
     }
 
     private void setup() {
+        Preconditions.checkState(isOnMainThread(), "Must be called from Minecraft thread.");
+
         //#if MC>=11100
         mc.inGameHud.getChatHud().clear(false);
         //#else