Fix renew output panic

MERGE REQUEST

Overview

This MR is an alternative solution to the siad panic to the one in !4264 (closed). It adds getters and setter to the FileContract and FileContractRevision to prevent out of bounds errors.

Example for Visual Changes

Checklist

Review and complete the checklist to ensure that the MR is complete before assigned to an approver.

• All new methods or updated methods have clear docstrings
• Testing added or updated for new methods
• Any new packages are added to Makefile and .gitlab-ci.yml
• API documentation updated for API updates
• Module README.md updated for changes to workflow
• Issue added to Sia-UI repo for new supporting features
• Changelog File Created

Issues Closed

Closes #3941 (closed)