[mod_dirlisting] fix logic inversion in cache
[mod_dirlisting] fix logic inversion in cache

Incorrect Content-Type returned for cached dirlisting
(bug in lighttpd 1.4.62 and lighttpd 1.4.63)

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4