Added support for anonymous structs/unions on compilers that implement it.

diff --git a/dlls/comctl32/comctl32undoc.c b/dlls/comctl32/comctl32undoc.c
index 416d35d..dc55648 100644
--- a/dlls/comctl32/comctl32undoc.c
+++ b/dlls/comctl32/comctl32undoc.c
@@ -89,8 +89,8 @@
 
     *phDpa = (HDPA)NULL;
 
-    position.LowPart = 0;
-    position.HighPart = 0;
+    position.s.LowPart = 0;
+    position.s.HighPart = 0;
 
     errCode = IStream_Seek (pStream, position, STREAM_SEEK_CUR, &newPosition);
     if (errCode != S_OK)