dlna_rules: add missing array sentinel.

these would trigger an invalid memory access during loop that looks
for curr->dlna_profile != NULL as the pointer would be undefined.
mp4 and generic: produce codec string with "p" prefix for profile.

we do match for "-p" to search profile, thus we must prefix the
profile string with "p" otherwise it won't match in DLNA processing.
fix buffer overflow if slen = 32.
fix test for SKIPPED entries.
include "itime" in the master/slave communication.
fix unsigned integer comparison in read() == size statements.