special case air in color calculations, this will prevent inappropria…

…tely register handlers from crashing when they receive air.

src/main/java/mod/chiselsandbits/render/helpers/ModelUtil.java

@@ -582,6 +582,12 @@ public static Integer getItemStackColor(
 			final ItemStack target,
 			final int tint )
 	{
+		// don't send air though to MC, some mods have registered their custom
+		// color handlers for it and it can crash.
+
+		if ( ModUtil.isEmpty( target ) )
+			return -1;
+
 		return Minecraft.getMinecraft().getItemColors().getColorFromItemstack( target, tint );
 	}