Memory leak bug fix for rc file parsing of invalid data

Memory leak bug fix for rc file parsing of invalid data

This commit fixes the following (found with the test suite in valgrind mode):

568 bytes in 1 blocks are still reachable in loss record 1 of 1
   at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x50B1C9A: __fopen_internal (iofopen.c:76)
   by 0x10D0CD: process_rc (config_init.c:516)
   by 0x10D645: config_init (config_init.c:752)
   by 0x10AB13: main (fwknop.c:70)