[ruby/io-console] Fix timeout type error (#18)

Fixed TypeError when IO#getch timed out

`rb_io_wait` returns a bit-flags Integer representing available
events, or Qfalse if timed out.  Also the result of `NUM2INT` is
not a `VALUE`.

```
$ ./bin/ruby -v -rio/console -e "p IO.console.getch(intr: true, time: 0.1)"
ruby 3.0.0dev (2020-10-09T20:27:30Z master 5ea2ea74cc) [x64-mingw32]
-e:1:in `getch': no implicit conversion of false into Integer (TypeError)
        from -e:1:in `<main>'
```

https://github.com/ruby/io-console/commit/3bdfaf62df

ext/io/console/console.c

@@ -546,7 +546,7 @@ console_getch(int argc, VALUE *argv, VALUE io)
 	    if (w < 0) rb_eof_error();
 	    if (!(w & RB_WAITFD_IN)) return Qnil;
 # else
-	    VALUE result = RB_NUM2INT(rb_io_wait(io, RUBY_IO_READABLE, timeout));
+	    VALUE result = rb_io_wait(io, RUBY_IO_READABLE, timeout);
 	    if (result == Qfalse) return Qnil;
 # endif
 	}

test/io/console/test_io_console.rb

@@ -471,6 +471,10 @@ defined?(IO.console) and TestIO_Console.class_eval do
     ensure
       IO.console(:close)
     end
+
+    def test_getch_timeout
+      assert_nil(IO.console.getch(intr: true, time: 0.1, min: 0))
+    end
   end
 end