Add an explicit exit 0 to the end of the script.

The implicit return is "$?", which can be set non-zero by
an earlier command.

src/zfs-auto-snapshot.sh

@@ -508,4 +508,5 @@ done
 print_log notice "@$SNAPSHOT_NAME, \
 $SNAPSHOT_COUNT created, $DESTRUCTION_COUNT destroyed, $WARNING_COUNT warnings."
 
+exit 0
 # }