fix: fields initialized

[Becheler]

#496

Before submitting

• This PR targets the develop branch.
• I searched for an existing PR or issue covering the same change.
• My contribution is licensed under the Boost Software License 1.0.

Type of change

• Bug fix
• New feature or API addition
• Refactor (no behavior change)
• Documentation
• Build, CI, or tooling
• Other (specify below)

Does this PR introduce a breaking change?

• Yes (describe migration impact below)
• No

What this PR does

Initalize fields to solve multiple -Wmissing-field-initializers

Motivation

Testing

Checklist

• Existing tests pass (b2 in the test/ directory).
• New behavior is covered by a test, or this is a docs / build / refactor change.
• Documentation was updated if user-facing behavior changed.
• No new compiler warnings on the platforms I built against.

[github-actions]

Boost dependency footprint vs develop (auto-generated).
PR run 31387073532 vs develop run 31385980713 (512d8b5f42).

Header-inclusion weights (graph files pulling each direct dependency in):

No header-inclusion-weight changes.

Transitive Boost modules: 68 → 68 (0)

[github-actions]

Compiler-warning counts vs develop (auto-generated).
PR run 31387073704 vs develop run 31385980794 (512d8b5f42).

Job	Baseline	After	Delta
macos (clang, 14)	681	668	-13
macos (clang, 17)	641	628	-13
macos (clang, 20)	641	628	-13
ubuntu (clang-19, 14)	681	668	-13
ubuntu (clang-19, 17)	641	628	-13
ubuntu (clang-19, 20)	641	628	-13
ubuntu (clang-19, 23)	641	628	-13
ubuntu (gcc-14, 14)	827	800	-27
ubuntu (gcc-14, 17)	949	922	-27
ubuntu (gcc-14, 20)	949	922	-27
ubuntu (gcc-14, 23)	949	922	-27
windows_msvc_14_3 (msvc-14.3)	962	962	0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.80%. Comparing base (bc05361) to head (512d8b5).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #553      +/-   ##
===========================================
+ Coverage    88.22%   92.80%   +4.58%     
===========================================
  Files          392      392              
  Lines        27412    28174     +762     
  Branches      7997     7997              
===========================================
+ Hits         24183    26147    +1964     
- Misses        1881     1922      +41     
+ Partials      1348      105    -1243     

Files with missing lines	Coverage Δ
test/graphviz_test.cpp	96.44% <ø> (+8.60%)	⬆️

... and 288 files with indirect coverage changes

---

Continue to review full report in Codecov by Harness.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0e818d4...512d8b5. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.