mod_disk_cache: Make sure that only positive integers are accepted

for the CacheMaxFileSize and CacheMinFileSize parameters in the
config file. PR39380 [Niklas Edmundsson <nikke acc.umu.se>]


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@450042 13f79535-47bb-0310-9956-ffa450edef68