No need for this assert.
uv_is_closing already checks for UV_HANDLE_CLOSED.
loop doesn't exist, we need to address it via the handle
Move req_connect field to main stream struct.

Makes the resulting code more readable, because we don't need conversations
any more.
Line too long.
return ENOTCONN if we write before connect.
set connect_req even if we succeed immediately.
remove unused variable.
The caller of this function expects a Windows error, not a libuv error.
consistency
Set only on default case.