Error handling: Undefined exception on out of bounds edit ID

[frolino]

For the edit functionality, the URL is of the following form

http://devsaran.github.io/contact-manager-backbone/#contacts/edit/{id}

where {id} is a numerical value. If the URL is manually changed to have an out of bounds {id}, an undefined error exception is thrown in the JavaScript code, instead of handling the out of bounds ID gracefully.