Catch issue with empty project.json

[jansepar]

If you go into test/fixtures-build (as of commit ref 644c87a), and run "mobify preview", the following error happens:

Shawns-MacBook-Air:fixtures-build shawnjan$ mobify preview
Unexpected Error.
Please report this error to https://cloud.mobify.com/support/

SyntaxError: Unexpected end of input
at Object.parse (native)
at Function.load (/usr/local/lib/node_modules/mobify-client/src/project.coffee:48:26)
at Command. (/usr/local/lib/node_modules/mobify-client/src/mobify.coffee:37:25)
at Command. (/usr/local/lib/node_modules/mobify-client/node_modules/commander/lib/commander.js:232:8)
at Command.emit (events.js:88:20)
at Command.parseArgs (/usr/local/lib/node_modules/mobify-client/node_modules/commander/lib/commander.js:399:12)
at Command.parse (/usr/local/lib/node_modules/mobify-client/node_modules/commander/lib/commander.js:349:15)
at Object. (/usr/local/lib/node_modules/mobify-client/src/mobify.coffee:227:11)
at Object. (/usr/local/lib/node_modules/mobify-client/src/mobify.coffee:233:4)
at Module._compile (module.js:432:26)

The project.json file is empty here, and I suspect this is why the error is happening.