Avoid bogus assert after calling wxDatePickerCtrl::SetRange() in wxMSW.

If the old value didn't lie inside the new range, it was changed by the native
control internally but the value stored by wxDatePickerCtrl itself remained
unchanged, resulting in asserts later when the mismatch between them was
detected.

Closes #13189.

src/msw/datectrl.cpp

@@ -138,9 +138,8 @@ void wxDatePickerCtrl::SetValue(const wxDateTime& dt)
         m_date.ResetTime();
 }
 
-wxDateTime wxDatePickerCtrl::GetValue() const
+wxDateTime wxDatePickerCtrl::MSWGetControlValue() const
 {
-#if wxDEBUG_LEVEL
     wxDateTime dt;
     SYSTEMTIME st;
     if ( DateTime_GetSystemtime(GetHwnd(), &st) == GDT_VALID )
@@ -148,6 +147,14 @@ wxDateTime wxDatePickerCtrl::GetValue() const
         dt.SetFromMSWSysDate(st);
     }
 
+    return dt;
+}
+
+wxDateTime wxDatePickerCtrl::GetValue() const
+{
+#if wxDEBUG_LEVEL
+    const wxDateTime dt = MSWGetControlValue();
+
     wxASSERT_MSG( m_date.IsValid() == dt.IsValid() &&
                     (!dt.IsValid() || dt == m_date),
                   wxT("bug in wxDateTimePickerCtrl: m_date not in sync") );
@@ -176,7 +183,12 @@ void wxDatePickerCtrl::SetRange(const wxDateTime& dt1, const wxDateTime& dt2)
     if ( !DateTime_SetRange(GetHwnd(), flags, st) )
     {
         wxLogDebug(wxT("DateTime_SetRange() failed"));
+        return;
     }
+
+    // Setting the range could have changed the current control value if the
+    // old one wasn't inside the new range, so update it.
+    m_date = MSWGetControlValue();
 }
 
 bool wxDatePickerCtrl::GetRange(wxDateTime *dt1, wxDateTime *dt2) const