Close callback being called multiple times when location changes

[DougKeller]

TL;DR: If the location changes while waiting on an async operation before closing a modal, the cleanUpClose function is invoked multiple times, resulting in an exception:

TypeError: Cannot read property 'resolve' of null (line 206 of angular-modal-service.js)

Steps to Reproduce

1. perform an async operation within a modal's controller, closing the modal once it's complete

   // ModalController
   $http.post('something').then(() => {
   close();
   });

2. While the request is running, go to a different url

   $location.path('/some-other-url');

   • $locationChangeSuccess is broadcasted, which closes the modal
3. async operation finishes
   • $http.post promise is resolved, causing close to be called
   • Because cleanUpClose was called already and set everything to null, the above exception is raised