Don't fail if ENV['ember-modal-dialog'] is not defined
Don't fail if ENV['ember-modal-dialog'] is not defined

- Hopefully restores working order in Ember Twiddle. Fixes #198.

oscarni/ember-modal-dialog,yapplabs/ember-modal-dialog,oscarni/ember-modal-dialog,yapplabs/ember-modal-dialog,samselikoff/ember-modal-dialog,samselikoff/ember-modal-dialog