Parenthesize graphIO ternary condition

[WilliamK112]

Summary

• add explicit grouping around the zero-based storage check used by the LEDA reader in the planarity package copy of graphIO.c
• keep the change limited to the warning-remediation expression described in Remediate package build warnings from graphIO.c #62
• leave the canonical EAPS graphIO.c counterpart for a follow-up because that file is currently part of Fix 0-based digraph adjacency list reads edge-addition-planarity-suite#275

Refs #62.

Tests

• git diff --check
• gcc -std=c99 -Wall -Wextra -Wparentheses -Werror -Wno-unused-parameter -I planarity/c/graphLib -I planarity/c/graphLib/lowLevelUtils -I planarity/c/graphLib/io -I planarity/c/graphLib/extensionSystem -I planarity/c/graphLib/planarityRelated -I planarity/c/graphLib/homeomorphSearch -c planarity/c/graphLib/io/graphIO.c -o %TEMP%\planarity-graphio-62\graphIO.o
• python setup.py sdist --dist-dir %TEMP%\planarity-sdist-62

Not run locally: wheel build / pytest, because this Windows shell does not have MSVC Build Tools available. python -m build --sdist --wheel reached bdist_wheel and then stopped with Microsoft Visual C++ 14.0 or greater is required.