Fix minor issues and add regress test

[yosuke-wolfssl]

This PR fixes the following issues:

• Fix ParseConfigLine to use correct idx
• Harden GetOpenSshKey to return error for wrong padded key
• Fix return code clobbers in src/keygen.c

Also, this adds a unit test for wrong padded OpenSSH key scenario.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR addresses a few correctness issues in config parsing and key handling, and adds a regression test to ensure malformed OpenSSH padding is rejected.

Changes:

• Fix whitespace-counting bounds in ParseConfigLine by using the correct remaining-length calculation.
• Harden OpenSSH private key parsing to fail on invalid padding.
• Prevent keygen cleanup failures from overwriting earlier return codes, and add a unit test for the bad-padding case.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
tests/api.c	Adds a malformed OpenSSH ECDSA key fixture and a regression test asserting it is rejected.
src/keygen.c	Avoids overwriting earlier errors with cleanup errors during RSA/ECDSA/Ed25519 key generation.
src/internal.c	Marks invalid OpenSSH padding as a key-format error during parsing.
apps/wolfsshd/configuration.c	Fixes an index/length bug when scanning whitespace for config values.

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