Prevent handle invalid output

[vitormattos]

Prevent to handle $output var with invalid value. If $output is empty or haven't version string, will return empty version.

I identified maybe a specific scenario with exec command when the $ouput get a delay to get the output of command and in this case the $output will be empty.

I thought about putting a delay like the follow code to prevent this problem. But, I did this with success, this looked like a more strange workaround to solve the problem. Because of this, I did the more simple, only checking if $output have the expected value.

\exec($command, $output);
$loop = 0;
while (empty($output) && $loop < 5) {
    usleep(500000);
    $loop++;
}

Maybe, the suggested code here can solve definitively the problem. Waiting for opinions from code review.

Still in time, the scenario in that I found this edge case was in a setup flow when I download the JSignPdf and with other process I do a loop waiting for finish download to check the downloaded version.