check_files.pl - -a without WARNING value always returns WARNING

[mbirth]

Running check_files.pl with the -a (age) option and specifying ~ as warning value, the check always returns WARNING if there's no file exceeding the CRITICAL age:

$ ./check_files.pl -D /mnt/myfolder/ -F "*.mxf" -a ~,300 -c 20 -f -T files
WARNING - testfile.mxf  is 6 (more than ) seconds old | '*.mxf'=1;;20 age_oldest=6s;;300 age_newest=6s