Fix issue in reject_if method on Event caused by blank dates in form

* A user clicks the Add Another Date link
* Then clicks the Add Another Time link (this will result in an id dynamically assigned to the new input field that is not zero)
* Then leaves both new fields blank in the dynamically added/created form (primary and secondary)
* When these blank request params get converted to a hash the has key will be whatever number was generated when the fields were added
* The reject_if method on Event was making the erroneous assumption that this value would always be "0"

* https://trello.com/c/yWAUd4tt