Double-check free memory after selecting victim pid
Double-check free memory after selecting victim pid

The run time of find_largest_process is proportional to the number
of processes, and takes 2.5ms on my box with a running Gnome desktop (try "make bench").
This is long enough that the situation may have changed in the meantime,
so we double-check if we still need to kill anything.
The run time of parse_meminfo is only 6us on my box and independent of the number
of processes (try "make bench").

Fixes https://github.com/rfjakob/earlyoom/issues/205

rfjakob/earlyoom,rfjakob/earlyoom,rfjakob/earlyoom,rfjakob/earlyoom