fix typo in mono_counters_cleanup leading to a double free

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
int a[0], malloc(0), memcpy(a,b,0), memcmp(c,d,0) doesn't make much sense

This remove a scan-build warning

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Merge pull request #897 from echampet/scanbuild

Scanbuild