Add error message when accessing 0th item
Add error message when accessing 0th item

See discussion in #58
mixonic/ember-cli-page-object,san650/ember-cli-page-object,san650/ember-cli-page-object,csantero/ember-cli-page-object,san650/ember-cli-page-object,csantero/ember-cli-page-object,mixonic/ember-cli-page-object