out_opentelemetry: Prevent null dereference on memcpy (CID 507910)

[cosmo0920]

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Testing
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• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

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• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

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Backporting

• Backport to latest stable release.

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