Fix for non-modal dialog closing.

diff --git a/include/dialog.h b/include/dialog.h
index ac3a14d..f340070 100644
--- a/include/dialog.h
+++ b/include/dialog.h
@@ -38,6 +38,7 @@
 #pragma pack(4)
 
 #define DF_END  0x0001
+#define DF_ENDING 0x0002
 
 extern BOOL32 DIALOG_Init(void);
 extern HWND32 DIALOG_CreateIndirect( HINSTANCE32 hInst, LPCSTR dlgTemplate,