[24365] Fix UB in serialization methods (backport #313)

[mergify]

Description

This PR fixes:

• UB error CdrSizeCalculator.hpp:1068:87: member call on null pointer of type 'const struct array' caused by an access to data->data() when size is 0.
• UB error Cdr.h:2976:77: runtime error: member call on null pointer of type 'const struct array' caused by an access to data->data() when size is 0.

Related PRs

• [24364 & 24365] Add UBSan workflow and solve its errors Fast-DDS#6386

Contributor Checklist

• Commit messages follow the project guidelines.
• The code follows the style guidelines of this project.
• Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A: Any new/modified methods have been properly documented using Doxygen.
• N/A: Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• N/A: Changes are API compatible.
• N/A: New feature has been added to the versions.md file (if applicable).
• N/A: Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• Check CI results: changes do not issue any warning.
• Check CI results: CI pass and failing tests are unrelated with the changes.

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This is an automatic backport of pull request #313 done by [Mergify](https://mergify.com).