[frontend] Replace use of strncpy with data()

Description

Fixes https://sonarcloud.io/project/security_hotspots?id=cern-cta_CTA&hotspots=AZqS8pNKeY_KLGES3aOz

Checklist

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

References

Closes #1363 (closed)