[GL Error Spam] Please check if key is unbound first

[pietro-lopes]

Check if key KeyMapping#isUnbound first to prevend logspam when this is unbound

[17:26:10] [Render thread/ERROR] [mojang/Window]: ########## GL ERROR ##########
[17:26:10] [Render thread/ERROR] [mojang/Window]: @ Pre render
[17:26:10] [Render thread/ERROR] [mojang/Window]: 65539: Invalid key -1

https://github.com/desht/ModularRouters/blob/1ef2e9652fd48823c9eb516db15f496503cb4f37/src/main/java/me/desht/modularrouters/client/util/ClientUtil.java#L71-L73