Description of problem:

In "cbreak" mode, ReadKey(-1) should return a pressed key or undefined
if no key was pressed. But the return value is always undefined even
if a key is pressed.

Version: perl-TermReadKey-2.20-7

How reproducible:

Always

Steps to Reproduce:
1. The following program should terminate after pressing a key:

#!/usr/bin/perl -w
use Term::ReadKey;
ReadMode 3;
while (not defined (ReadKey(-1))) {}
    
Actual results:
The program makes an endless loop no matter which key is pressed.

Expected results:
The program should terminate after pressing a key