Await graphql handler to avoid unhandled promise rejections

[shawnmcknight]

There are scenarios where the graphqlHandler function can reject. Notably, I have seen this when supplying an improperly formatted multipart request (e.g. invalid json). However, because the call to the graphql handler is not awaited, the catch which handles the error will not be invoked. Instead, this error will bubble out to moleculer-web which does not properly handle the rejected promise. This leads to an unhandled promise rejection in Node and, depending on node version, a hard failure of the NodeJS process.

The solution is to simply await the execution of the graphql handler. In this case, if the handler rejects, then the catch will be properly invoked and there will not be an unhandled promise rejection.

[icebob]

Thanks!