fix: handling 'undefined' from erlang:process_info/2

Process could die between the time we get its PID from erlang:processes() and
when we start calling erlang:process_info/2 on it; or even somewhere between
the process_info calls.

The choice is between returning partial info (that we were able to collect
before process died) and just skipping the process. For now, I'm choosing to
skip the process (throwing away any partial info collected).