Add GraphQLParser errors to verbose output (#2873)

* Add GraphQLParser errors to verbose output

Was having issues with a malformed graphql query due to the differences between allContentfulX and contentfulX mappings.  Very difficult to track down until I added the following GraphQLParser exception.  I've scoped this to only show if verbose output is turned on to ensure newbies have some reference while using graphql, without getting in anyone else's way.

* Update PR: return original error if formatted graphql error is empty

packages/gatsby/src/internal-plugins/query-runner/graphql-errors.js

@@ -176,18 +176,18 @@ export function graphqlError(
  )
  }
 
- message = `There was an error while compiling your site's GraphQL queries.
- ${message}
+ let reportedMessage = `There was an error while compiling your site's GraphQL queries.
+ ${message || error.message}
  `
+
  if (error.message.match(/must be an instance of/)) {
- message +=
+ reportedMessage +=
  `This usually means that more than one instance of 'graphql' is installed ` +
  `in your node_modules. Remove all but the top level one or run \`npm dedupe\` to fix it.`
  }
 
  if (error.message.match(/Duplicate document/)) {
- message += `${error.message.slice(21)}\n`
+ reportedMessage += `${error.message.slice(21)}\n`
  }
-
- return message
+ return reportedMessage
 }