Guard against instances where the GLWindow is closed without being opened (#Forge)

src/hdskins/java/com/voxelmodpack/hdskins/upload/GLWindow.java

@@ -1,10 +1,14 @@
 package com.voxelmodpack.hdskins.upload;
 
 import com.google.common.collect.Lists;
+import com.mumfrey.liteloader.util.ModUtilities;
 
 import net.minecraft.client.Minecraft;
 import net.minecraft.client.resources.DefaultResourcePack;
 import net.minecraft.util.ResourceLocation;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.lwjgl.LWJGLException;
 import org.lwjgl.opengl.Display;
 import org.lwjgl.opengl.DisplayMode;
@@ -38,6 +42,8 @@ public class GLWindow extends DropTarget {
     @Nullable
     private static GLWindow instance = null;
 
+    private static final Logger logger = LogManager.getLogger();
+
     /**
      * Gets or creates the current GLWindow context.
      */
@@ -162,6 +168,27 @@ public class GLWindow extends DropTarget {
     }
 
     private synchronized void close() {
+        if (frame == null) {
+            String msg = "GLClose was called in an illegal state! You cannot close the GLWindow before it has been opened.";
+
+            if (ModUtilities.fmlIsPresent()) {
+                logger.fatal("========================================================");
+                logger.fatal("!!!!!! MINECRAFT FORGE / FORGE MODLOADER DETECTED !!!!!!");
+                logger.fatal("FML was detected! Forge is known to cause severe incompatibilities and instability with other mods"
+                        + " above and beyond interfering with the normal functioning of existing game registries,"
+                        + " blocking system calls / AWT functions,"
+                        + " obfuscating/deobfuscating parts of minecraft and mod code."
+                        + " .jar signature invalidation"
+                        + " and/or deep and irreversible core modifications to the game.");
+                logger.fatal("A full stacktrace is provided below for debugging purposes.");
+                logger.fatal(msg, new IllegalStateException(msg));
+                logger.fatal("========================================================");
+            } else {
+                logger.fatal(msg);
+            }
+            return;
+        }
+
         closeRequested = true;
 
         try {