Removing draco wasm module stops engine example from loading

[mvaligursky]

Repro steps:

1. remove draco config code from multi-view or post-effects engine example:

        pc.WasmModule.setConfig('DracoDecoderModule', {
            glueUrl: '/static/lib/draco/draco.wasm.js',
            wasmUrl: '/static/lib/draco/draco.wasm.wasm',
            fallbackUrl: '/static/lib/draco/draco.js'
        });

2. reaload the example. The example does not load, nor we get any warnings / errors in the console. It seems the code is not even hitting this line in the glb-parser, where I assumed could be a problem:

     const decoderModule = dracoDecoderInstance || window.DracoDecoderModule;

I suspect our users might hit this in their applications, and logging some useful errors would be helpful.