DateTimeEditBox popup (MonthCalendar) crashes when Maximum is set to DateTime.MaxValue

Hi Guys,

As the title says, the DateTimeEditBox popup (i.e. MonthCalendar) crashes when Maximum is set to DateTime.MaxValue. This can be reproduced with:

<Page
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:sys="clr-namespace:System;assembly=mscorlib"
  xmlns:ae="clr-namespace:ActiproSoftware.Windows.Controls.Editors;assembly=ActiproSoftware.Editors.Wpf">
  <StackPanel>  
    <ae:DateTimeEditBox Maximum="{x:Static sys:DateTime.MaxValue}" Value="9999-10-31" />
  </StackPanel>
</Page>

Steps to reproduce:

1. Open the edit box's drop down. Still OK here.
2. Press the right arrow to move the month to November 9999. Still OK here.
3. Press the right arrow again to move the month to December 9999. Crashes here.

I suspect the crash occurs because MonthCalendar will try to generate the items for the next month (which is beyond DateTime's range).