trac#385: Missing version should not be fatal

We already handle @comment similarly.

Addressing:
    #0  0x000000391c03a997 in ____strtoll_l_internal () from /lib64/libc.so.6
    #1  0x000000391c0371d0 in atoi () from /lib64/libc.so.6
    #2  0x00007ffff7d20f52 in oval_test_parse_tag (reader=0x61eac0, context=0x7fffffffd840, usr=0x0) at oval_test.c:402
    #3  0x00007ffff7d151f4 in oval_parser_parse_tag (reader=0x61eac0, context=0x7fffffffd840, tag_parser=0x7ffff7d20d23 <oval_test_parse_tag>, user=0x0) at oval_parser.c:59
    #4  0x00007ffff7d156c8 in oval_definition_model_parse (reader=0x61eac0, context=0x7fffffffd840) at oval_parser.c:177
    #5  0x00007ffff7d057fb in oval_definition_model_merge (model=0x61ec20, file=0x61c9f0 "/var/tmp/1.xml") at oval_defModel.c:245
    #6  0x00007ffff7d056aa in oval_definition_model_import (file=0x61c9f0 "/var/tmp/1.xml") at oval_defModel.c:214
    #7  0x0000000000409c8c in app_evaluate_oval (action=0x7fffffffd990) at oscap-oval.c:390
    #8  0x0000000000407d21 in oscap_module_call (action=0x7fffffffd990) at oscap-tool.c:261
    #9  0x000000000040819e in oscap_module_process (module=0x616f00 <OVAL_EVAL>, argc=5, argv=0x7fffffffdc08) at oscap-tool.c:346
    #10 0x0000000000406b57 in main (argc=5, argv=0x7fffffffdc08) at oscap.c:79
Bump version after release.