Reset display_capabilities_ pointer after merging capabilities

[jacobkeeler]

Fixes #3800

This PR is ready for review.

Risk

This PR makes no API changes.

Testing Plan

Manually test using instructions in #3800

Summary

Currently set_display_capabilities overwrites the display capabilities, then merges them with the previous capabilities, this PR changes this process to merge them first, then overwrite the capabilities

Changelog

Bug Fixes

• Resets displaycapabilities pointer after merging capabilities, rather than before

CLA

• [x] I have signed the CLA