winmm: Accept the ancient, smaller MIDIHDR.
diff --git a/include/mmsystem.h b/include/mmsystem.h
index dd9723a..d147bf3 100644
--- a/include/mmsystem.h
+++ b/include/mmsystem.h
@@ -718,6 +718,7 @@
     DWORD	dwFlags;
     struct midihdr_tag *lpNext;
     DWORD_PTR	reserved;
+    /* Win 32 extended the structure with these 2 fields */
     DWORD	dwOffset;
     DWORD_PTR	dwReserved[8];
 } MIDIHDR, *LPMIDIHDR;