Apparently there is a quirk of GetWindowLongPtr when querying styles. If
the style bits are genuinely 0, the API returns 0 but does not clear the
last error.
If a previous API call set an error, GetWindowLongPtr might define
"failure" as "return 0 AND GetLastError != 0".
Hence, it is important to clear the last/previous error before calling
GetWindowLongPtrW to ensure that we don't misinterpret a valid 0 return
value as an error.
