Describe the bug
Calling Children() on a process without child processes returns a non-nil err

the source code uses common.CallPgrepWithContext which calls pgrep -P $PID. If input pid is without child processes, pgrep exit code is 1, the function call returns error with exits status 1

To Reproduce

// paste example code reproducing the bug you are reporting

Expected behavior
The function should return ErrorNoChildren?

Environment (please complete the following information):

• Windows: [paste the result of ver]
• Linux: [paste contents of /etc/os-release and the result of uname -a]
• Mac OS: [paste the result of sw_vers and uname -a
• FreeBSD: [paste the result of freebsd-version -k -r -u and uname -a]
• OpenBSD: [paste the result of uname -a]

Additional context
[Cross-compiling? Paste the command you are using to cross-compile and the result of the corresponding go env]