Add support for wxDatePickerCtrl::SetNullText() to XRC

Recognize null-text element.

misc/schema/xrc_schema.rnc

@@ -894,7 +894,8 @@ wxDatePickerCtrl =
     element object {
         attribute class { "wxDatePickerCtrl" } &
         stdObjectNodeAttributes &
-        stdWindowProperties
+        stdWindowProperties &
+        [xrc:p="o"] element null-text {_, t_text }*
     }
 
 

src/xrc/xh_datectrl.cpp

@@ -42,6 +42,10 @@ wxObject *wxDateCtrlXmlHandler::DoCreateResource()
 
     SetupWindow(picker);
 
+    // Note that we want to set this one even if it's empty.
+    if ( HasParam(wxS("null-text")) )
+        picker->SetNullText(GetText(wxS("null-text")));
+
     return picker;
 }