Add missing clear when deserializing maps

[fschoenm]

Description

See the linked Fast-DDS issue. In certain deserialization scenarios, a receiving map is not cleared which leads to an object containing random data from a previous message.

Fixes eProsima/Fast-DDS#5136

Contributor Checklist

• [x] Commit messages follow the project guidelines.
• [x] 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
• [x] Any new/modified methods have been properly documented using Doxygen.
• [x] Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• [x] Changes are API compatible.
• [ ] New feature has been added to the versions.md file (if applicable).
• [ ] 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.

[Mario-DL]

@fschoenm thanks for the contribution ! I have opened #233 in order to avoid problems with external contributions and ci. It also adds a test. Closing this PR in favor of the other.