handle NULL BSTRs as empty ones per Microsoft convention

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@50027 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/ole/oleutils.cpp

@@ -75,6 +75,11 @@ WXDLLEXPORT BSTR wxConvertStringToOle(const wxString& str)
 
 WXDLLEXPORT wxString wxConvertStringFromOle(BSTR bStr)
 {
+    // NULL BSTR is equivalent to an empty string (this is the convention used
+    // by VB and hence we must follow it)
+    if ( !bStr )
+        return wxString();
+
 #if wxUSE_UNICODE
     wxString str(bStr);
 #else