Fix record parser when the FLAGS item is omitted

[dajiaohuang]

This PR fixes #118

Problem

The record parser accepts item flag combinations that omit the FLAGS field, but parse_line unconditionally parsed that missing field and raised TypeError.

Changes

• Parse FLAGS only when the field is present.
• Add a regression test for a valid record containing only the operation type.

Verification

• python -m unittest test_record_parser.py
• python -m py_compile record_parser.py test_record_parser.py
• python record_parser.py -f 000000000100 -l hook_func_addr

[caikelun]

Thanks. Please update your PR: keep only the changes to tools/record_parser.py.
(I don't think it's necessary to keep a Python script in the project specifically for testing this bug.)

[dajiaohuang]

Updated in c78453e: I removed tools/test_record_parser.py, so the PR now changes only tools/record_parser.py.

Validation:

• python -m py_compile tools/record_parser.py
• exercised the missing-FLAGS parse_line() path with a local import stub for the unavailable capstone dependency; it produced the expected operation output
• git diff --check upstream/dev...HEAD

The full CLI command could not run in this environment because capstone is not installed.