Description:
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I set up my USB Serial Device as COMx (COM1-COM9) and everything works fine.
But if I change it to a number with more than one digit, it shows me a warning which says 'Invalid Argument'.

Test script:
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<?php

//both exec work
//exec('mode com6: baud=115200 data=8 stop=1 parity=n xon=off dtr=off rts=off');
exec('mode com11: baud=115200 data=8 stop=1 parity=n xon=off dtr=off rts=off');

//$fd = dio_open('com6:', O_RDWR); //<--works
$fd = dio_open('com11:', O_RDWR); //<-- dont work (invalid argument)

$command="\x11\x0E\x1B\x44\x4C\x1B\x47\x44\x00\x00\x00\x00\x3F\x01\xEF\x00\x9F\x00";
$len=17;

$bytes_written = dio_write($fd,$command,$len);

echo $bytes_written;

dio_close($fd);

?>

Expected result:
----------------
Using com6 -> the script echos 17

using com11 -> the script should echo 17

Actual result:
--------------
Using com6 -> the script echos 17

using com11 -> 
Warning: dio_open(): cannot open file com11: with flags 2 and permissions 0: Invalid argument in ...
Warning: dio_write() expects parameter 1 to be resource, boolean given in ...
Warning: dio_close() expects parameter 1 to be resource, boolean given in