Fix loading corrupted lwjgl3ify-early.json

[YannickMG]

There were 3 reports of this issue in the #help channel. This can happen when the server runs out of space and a zero-length lwjgl3ify-early.json is left behind.

A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
        at ...
Caused by: java.lang.NullPointerException: Cannot read field "extensibleEnums" because "cfg" is null
        at System//me.eigenraven.lwjgl3ify.rfb.EarlyConfig.load(EarlyConfig.java:100)
        at System//me.eigenraven.lwjgl3ify.rfb.Lwjgl3ifyRfbPlugin.onConstruction(Lwjgl3ifyRfbPlugin.java:37)
        at com.gtnewhorizons.retrofuturabootstrap.plugin.PluginLoader.initializePlugins(PluginLoader.java:112)
        at System//net.minecraft.launchwrapper.Launch.rfb$realLaunch(Launch.java:197)
        at System//net.minecraft.launchwrapper.Launch.launch(Launch.java:35)
        at System//net.minecraft.launchwrapper.Launch.main(Launch.java:60)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:568)
        at com.gtnewhorizons.retrofuturabootstrap.Main.main(Main.java:207)
        ... 6 more

By the way, is writing this file at startup rather than distributing a config file for it actually desirable?

[eigenraven]

Generating this file on startup is desired, because it contains OS-specific information like the cached list of java installations on the computer.