Correctly handle failure to read /proc/self/exe link

[robert-ancell]

Existing code would attempt to use the negative length to create a std::string.

Existing code was also returning an empty path when the length was > PATH_MAX. This was removed to match the code in engine/src/flutter/fml/platform/linux/paths_linux.cc

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

[robert-ancell]

Second part of #184476

[gemini-code-assist]

Code Review

This pull request modifies the Linux implementation of GetExecutableDirectory by reducing the buffer size and changing the error handling for readlink. Feedback suggests that these changes reduce robustness against path truncation; it is recommended to use a larger buffer and explicitly check for both errors and truncation to ensure the returned path is complete.

[loic-sharma]

LGTM!