TF26027: A field definition Microsoft.VSTS.Common.ClosedDate in the w…

…ork item type definition file does not exist. (#2455)

Some work items do not have this field...

Updated to:

```
if (newWorkItem.Fields.Contains("Microsoft.VSTS.Common.ClosedDate") && newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].IsEditable)
{
    newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].Value = oldWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].Value;
}
```

Related Disucssions:

-
#2086
-

src/MigrationTools.Clients.TfsObjectModel/Processors/TfsWorkItemMigrationProcessor.cs

@@ -419,12 +419,12 @@ private void PopulateWorkItem(WorkItemData oldWorkItemData, WorkItemData newWork
             }
 
             newWorkItem.Title = oldWorkItem.Title;
-            if (newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].IsEditable)
+            if (newWorkItem.Fields.Contains("Microsoft.VSTS.Common.ClosedDate") && newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].IsEditable)
             {
                 newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].Value = oldWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].Value;
             }
             newWorkItem.State = oldWorkItem.State;
-            if (newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].IsEditable)
+            if (newWorkItem.Fields.Contains("Microsoft.VSTS.Common.ClosedDate") && newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].IsEditable)
             {
                 newWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].Value = oldWorkItem.Fields["Microsoft.VSTS.Common.ClosedDate"].Value;
             }