windows: correcly signal PortClosed error on blocked Read()

This commit fix regression test TestConcurrentReadAndWrite.

Even if the test checks purpose is another it has detected
anyway that the returned error is incorrect.

Another specific test for closing port detection will be added
in the future.

serial_windows.go

@@ -82,14 +82,15 @@ func (port *windowsPort) Read(p []byte) (int, error) {
 	defer syscall.CloseHandle(ev.HEvent)
 	for {
 		err := syscall.ReadFile(port.handle, p, &readed, ev)
+		if err == syscall.ERROR_IO_PENDING {
+			err = getOverlappedResult(port.handle, ev, &readed, true)
+		}
 		switch err {
 		case nil:
 			// operation completed successfully
-		case syscall.ERROR_IO_PENDING:
-			// wait for overlapped I/O to complete
-			if err := getOverlappedResult(port.handle, ev, &readed, true); err != nil {
-				return int(readed), err
-			}
+		case syscall.ERROR_OPERATION_ABORTED:
+			// port may have been closed
+			return int(readed), &PortError{code: PortClosed, causedBy: err}
 		default:
 			// error happened
 			return int(readed), err