correctly scope liquidjs errors

[nagibyro]

Fix for #243. When the liquidjs engine throws an error the scope of the catch block has reply.send as undefined. this swallows the liquidjs error. This PR fixes the scoping issue and allows liquid js errors to be sent by fastify correctly.

I'm not sure why https://github.com/fastify/point-of-view/blob/master/test/test-liquid.js#L439 doesn't catch this error. the error my code actually was getting from liquidjs was err.message = 'ENOENT: Failed to lookup "${file}" in "${roots}"'; I added a test to check this error but I couldn't make it fail before I made the change so not sure if it really helps.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm

[climba03003]

LGTM.