Adding tasks work, but rolling back new-task-transaction fails :(
"Fix" for rolling back new-task-transaction rollback.

Without this, when I try to roll back the transaction created by the
tables controller when adding a new task will fail with:

Uncaught TypeError: Cannot call method 'hasOwnProperty' of undefined

application.js:44396
DS.JSONSerializer.DS.Serializer.extend.extractId application.js:44396
DS.Serializer.Ember.Object.extend.materialize application.js:43776
DS.Adapter.Ember.Object.extend.materialize application.js:45184
DS.Store.Ember.Object.extend.materializeData application.js:39085
DS.Model.Ember.Object.extend.materializeData application.js:41609
DS.Model.Ember.Object.extend.data application.js:41600
ComputedPropertyPrototype.get application.js:15395
get application.js:13807
getAttr application.js:41969
(anonymous function) application.js:41994
ComputedPropertyPrototype.get application.js:15395
get application.js:13807
Ember.Observable.Ember.Mixin.create.get application.js:21164
Todo.Task.DS.Model.extend.minutesLeftToComplete application.js:45926
ComputedPropertyPrototype.get application.js:15395
get application.js:13807
(anonymous function) application.js:19440
(anonymous function) application.js:19425
Ember.Enumerable.Ember.Mixin.create.forEach application.js:19360
Ember.Enumerable.Ember.Mixin.create.map application.js:19424
Ember.Enumerable.Ember.Mixin.create.mapProperty application.js:19439
Ember.Enumerable.Ember.Mixin.create.getEach application.js:19376
Todo.List.DS.Model.extend.minutesLeftToComplete application.js:45902
ComputedPropertyPrototype.get application.js:15395
get application.js:13807
Ember.ObjectProxy.Ember.Object.extend.unknownProperty
application.js:23395
get application.js:13817
Ember.Observable.Ember.Mixin.create.get application.js:21164
Todo.ListController.Ember.ObjectController.extend.isNotCompleted
application.js:45946
ComputedPropertyPrototype.get application.js:15395
get application.js:13807
Ember.Handlebars.get application.js:29466
observer application.js:30609
(anonymous function) application.js:16004
Ember.handleErrors application.js:12357
invoke application.js:16002
invokeOnceTimer application.js:16447
(anonymous function) application.js:16004
Ember.handleErrors application.js:12357
invoke application.js:16002
iter application.js:16074
RunLoop.flush application.js:16128
RunLoop.end application.js:16033
tryable application.js:16237
Ember.tryFinally application.js:12995
Ember.run.end application.js:16240
autorun
Bugfix in list model when calculating minutesLeftToComplete.

..must parseInt the min-value, as it is a string when it is set on a new
record from the form.