Plug a memory leak.

Addressing:
568 bytes in 1 blocks are still reachable in loss record 1 of 1
   at 0x4A0645D: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x3C2B46C17C: __fopen_internal (iofopen.c:73)
   by 0x4C63FEC: bz2_open (bz2.c:49)
   by 0x4C641D1: bz2_read_doc (bz2.c:97)
   by 0x4C6499B: oscap_source_get_xmlDoc (oscap_source.c:143)
   by 0x4C6483B: oscap_source_get_xmlTextReader (oscap_source.c:110)
   by 0x4C648E4: oscap_source_get_scap_type (oscap_source.c:125)
   by 0x40E226: app_info (oscap-info.c:81)
   by 0x407E28: oscap_module_call (oscap-tool.c:260)
   by 0x4082A5: oscap_module_process (oscap-tool.c:345)
   by 0x406CB6: main (oscap.c:80)
LEAK SUMMARY:
   definitely lost: 0 bytes in 0 blocks
   indirectly lost: 0 bytes in 0 blocks
     possibly lost: 0 bytes in 0 blocks
   still reachable: 568 bytes in 1 blocks
        suppressed: 0 bytes in 0 blocks