range is set (or only one of the bounds is set), @a dt1 and/or @a dt2
are set to be invalid.
+ Notice that when using a native MSW implementation of this control the
+ lower range is always set, even if SetRange() hadn't been called
+ explicitly, as the native control only supports dates later than year
+ 1601.
+
@param dt1
Pointer to the object which receives the lower range limit or
becomes invalid if it is not set. May be @NULL if the caller is not