cache: cache_record_find: fix buffer overflow

cache: cache_record_find: fix buffer overflow

Fixes following buffer overflow:

 ERROR: AddressSanitizer: global-buffer-overflow on address 0x0000007338b8 at pc 0x0000004db339 bp 0x7ffe370e6140 sp 0x7ffe370e6138
 READ of size 8 at 0x0000007338b8 thread T0
     #0 0x4db338 in cache_record_find mdnsd/cache.c:197:17
     #1 0x4d74b4 in cache_answer mdnsd/cache.c:336:6
     #2 0x4cf04a in parse_answer mdnsd/dns.c:343:3
     #3 0x4cb272 in dns_handle_packet mdnsd/dns.c:442:7
     #4 0x4f508c in read_socket4 mdnsd/interface.c:253:3
     #5 0x7fb81dddc73d in uloop_run_events libubox/uloop.c:198:4
     #6 0x7fb81dddc73d in uloop_run_timeout libubox/uloop.c:555:3
     #7 0x4c77cd in uloop_run libubox/uloop.h:111:9
     #8 0x4c7757 in main mdnsd/main.c:99:2

 0x0000007338b8 is located 8 bytes to the right of global variable 'records' defined in 'mdnsd/cache.c:45:1' (0x733880) of size 48
 SUMMARY: AddressSanitizer: global-buffer-overflow mdnsd/cache.c:197:17 in cache_record_find

Signed-off-by: Petr Štetiar <ynezz@true.cz>