[Misc] Apply SonarCloud rule cpp:S4962

Description

• Remove extraneous brackets from return statements in the mediachanger code
• Minor refactor of a couple of branch constructs that were hard to read
• Replace all NULL with nullptr (rule cpp:S4962)

Checklist

• Documentation reflects the changes made.
• Merge Request title is clear, concise, and suitable as a changelog entry. See our contributing docs

References

Closes #1371 (closed)