Try/catch around pcbStackup function

[kasbah]

Relating to errors like mcous/gerber-plotter#14, I think we need to try {} catch e {reject(e)} around pcbStackup here in case it does crash.

[mcous]

Given that gerber-plotter operates asynchronously in a stream, I don't think try-catch will work. Just a hunch, but heads up

[ju5t]

It doesn't catch the error from mcous/gerber-plotter#14 but it's still useful.

[kasbah]

I was thinking about it a bit more after I opened this. I think it would reject the promise on a normal error anyway.

@mcous, maybe something could be done in gerber-to-svg or dependencies to better recover from errors within the stream processing?

[ju5t]

I was thinking about it a bit more after I opened this. I think it would reject the promise on a normal error anyway.

Arguably the current try/catch-block is a bit large. It doesn't do much harm at the moment though so I believe it can stay as it is. Additional error handling can be added when they are found and not caught in the current solution.