[BUG] Logger Must Always NUL-Terminate on No-Arg Path

[k8ika0s]

Proposed PR branch: qe/issue-04-logger-nul-termination

Category: Bug (potential memory disclosure / UB hardening)

Problem

• Logger path when log_message() is called without extra args must guarantee
  NUL termination to avoid undefined reads and garbage/log leakage.

Justification / why this is needed

• Unterminated strings can cause reads past the intended buffer, which is UB
  and can leak memory contents into logs (a confidentiality concern).
• Logging code is often enabled during failures; that’s the worst time to risk
  adding more instability or leaking unrelated memory.

Proposed change

• Guarantee NUL termination on the no-arg path.
• Add a regression test that would fail if truncation/untermination occurs.

Acceptance criteria

• Log strings are always NUL-terminated regardless of arg path.
• Regression test covers the fixed behavior.

Test plan

• make test (expects tests/testDriver_logger_nul_termination.c to pass).

References

• Key files: zdnn/logger.c, tests/testDriver_logger_nul_termination.c.