oleaut: Fix VarFormat for VT_NULL variants.

dlls/oleaut32/tests/vartest.c

@@ -1785,10 +1785,8 @@ static void test_VarFormat(void)
   /* VT_NULL */
   V_VT(&in) = VT_NULL;
   hres = pVarFormat(&in,NULL,fd,fw,0,&out);
-  todo_wine {
   ok(hres == S_OK, "VarFormat failed with 0x%08lx\n", hres);
   ok(out == NULL, "expected NULL formatted string\n");
-  }
 
   /* Invalid args */
   hres = pVarFormat(&in,NULL,fd,fw,flags,NULL);

dlls/oleaut32/varformat.c

@@ -2007,6 +2007,9 @@ HRESULT WINAPI VarFormatFromTokens(LPVARIANT pVarIn, LPOLESTR lpszFormat,
   if (!pVarIn || !rgbTok)
     return E_INVALIDARG;
 
+  if (V_VT(pVarIn) == VT_NULL)
+    return S_OK;
+
   if (*rgbTok == FMT_TO_STRING || header->type == FMT_TYPE_GENERAL)
   {
     /* According to MSDN, general format acts somewhat like the 'Str'