Making sure serialize_buffer properly destroys buffer, if needed.

[hkaiser]

Fixes #6366

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
-0.03%	65.35%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (103a7b8)	190583	162311	85.17%
Head commit (c62a6ea)	190573 (-10)	162243 (-68)	85.13% (-0.03%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#6368)	101	66	65.35%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[hkaiser]

retest lsu

[hkaiser]

bors merge

[bors]

This PR was included in a batch that successfully built, but then failed to merge into master. It will not be retried.

Additional information:

Response status code: 422
{"message":"Changes must be made through a pull request.","documentation_url":"https://docs.github.com/articles/about-protected-branches"}