Small chance Process.children() may swallow AccessDenied on Linux

[giampaolo]

Right now EPERM / AccessDenied exceptions are swallowed, meaning children() may return less results:

psutil/psutil/_pslinux.py

Line 1385 in bf79914

errno.EPERM, errno.EACCES):

This is highly unlikely as /proc/pid/stat should always be readable. Still, the code should raise the exception instead of ignoring it.