OpenBSD: Process.cmdline() may raise SystemError

[giampaolo]

======================================================================
ERROR: psutil.tests.test_process.TestProcess.test_zombie_process
----------------------------------------------------------------------
ProcessLookupError: [Errno 3] No such process

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/vagrant/psutil/psutil/tests/test_process.py", line 1281, in test_zombie_process
    zproc.as_dict()
  File "/vagrant/psutil/psutil/__init__.py", line 575, in as_dict
    ret = meth()
  File "/vagrant/psutil/psutil/__init__.py", line 696, in exe
    exe = self._proc.exe()
  File "/vagrant/psutil/psutil/_psbsd.py", line 496, in wrapper
    return fun(self, *args, **kwargs)
  File "/vagrant/psutil/psutil/_psbsd.py", line 577, in exe
    cmdline = self.cmdline()
  File "/vagrant/psutil/psutil/_psbsd.py", line 496, in wrapper
    return fun(self, *args, **kwargs)
  File "/vagrant/psutil/psutil/_psbsd.py", line 603, in cmdline
    return cext.proc_cmdline(self.pid)
SystemError: <class 'OSError'> returned a result with an error set

For some reason I saw this happening on Python 3.7 only.