[bugfix] avoid TypeError when resolving enqueued write requests from cache
Merge branch 'fix-writeerror' of github.com:jtomaszewski/angular-cached-resource into jtomaszewski-fix-writeerror

Conflicts:
	angular-cached-resource.js
	angular-cached-resource.min.js
	lib/resource_write_queue.js
	src/resource_write_queue.coffee