libcollectdclient: fix gcc warning

libcollectdclient: fix gcc warning

make[1]: Entering directory '/home/ruben/src/collectd'
  CC       src/libcollectdclient/libcollectdclient_la-network_parse.lo
In function ‘parse_string’,
    inlined from ‘parse_identifier’ at src/libcollectdclient/network_parse.c:169:7,
    inlined from ‘network_parse.constprop’ at src/libcollectdclient/network_parse.c:540:11:
src/libcollectdclient/network_parse.c:161:3: warning: ‘strncpy’ specified bound 64 equals destination size [-Wstringop-truncation]
   strncpy(out, in, out_size);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~