Updates the default errors. This method is required when errors are initialize via
InitializeDefaultErrors. This method checks whether default errors were added for a specific property (or at entity level if
propertyName is
string.Empty or
null
).
Reason for this is that if the error is known on forehand, the entity implementation will not raise the INotifyDataErrorInfo.ErrorsChanged event. If the default errors are cleared, the validation via INotifyDataErrorInfo.ErrorsChanged will take over from this point.