In device_issue_read() there is no need to reset Offset and OffsetHigh

In device_issue_read() there is no need to reset Offset and OffsetHigh
to 0; they are only used for seekable files (not sockets).

Reset the write event before the call to WriteFile().  This is
consistent with how the read event is reset before ReadFile().

Clear device_write_packet.len() if WriteFile() fails with an error
other than ERROR_IO_PENDING; otherwise write_packet() will call
GetOverlappedResult() the next time it is run even though there is
no write in progress.