Fix posix_kill crashing / killing other programs on null (#68) #183

# to view logs

Job	Run time
Coding standards (ubuntu-latest, 8.0, --ignore-platform-req=php)	27s
PHP 7.0 on ubuntu-latest	47s
PHP 7.1 on ubuntu-latest	55s
PHP 7.2 on ubuntu-latest	55s
PHP 7.3 on ubuntu-latest	1m 3s
PHP 7.4 on ubuntu-latest	1m 1s
PHP 8.0 on ubuntu-latest	50s
PHP 8.0 on windows-latest	1m 45s
PHP 8.0 on macos-latest	1m 18s
	9m 1s

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