Implement GetFileSizeEx compatibility wrapper

[Jookia]

Windows before 2000 lacks GetFileSizeEx which Rust relies on. Implement a compatibility function that uses GetFileSize as a backup.

[cher-nov]

Better call GetLastError() only on INVALID_FILE_SIZE.

Suggested change

	let mut high32 = 0;
	let low32 = unsafe { GetFileSize(hfile, &mut high32) };
	let full_size: u64 = ((high32 as u64) << 32) | (low32 as u64);
	let last_err = unsafe { GetLastError() };
	if low32 == INVALID_FILE_SIZE && last_err != NO_ERROR {
	return FALSE;
	} else {
	if !lpfilesize.is_null() {
	unsafe { *lpfilesize = full_size as i64; }
	}
	return TRUE;
	}
	}
	let mut high32 = 0;
	let low32 = unsafe { GetFileSize(hfile, &mut high32) };
	if low32 == INVALID_FILE_SIZE {
	let last_err = unsafe { GetLastError() };
	if last_err != NO_ERROR { return FALSE; }
	}
	if !lpfilesize.is_null() {
	let full_size: u64 = ((high32 as u64) << 32) | (low32 as u64);
	unsafe { *lpfilesize = full_size as i64; }
	}
	TRUE
	}

[cher-nov]

Also, worth noting that genuine GetFileSizeEx(, NULL) segfaults (at least on my Windows 7). It still makes sense to return TRUE instead if nothing else has gone wrong (just as ReactOS does, for example), but should we do at least SetLastError(ERROR_INVALID_PARAMETER) in that case? @seritools