Only send WARNINGS response for missing alert images if normal result is SUCCESS

[jacobkeeler]

Fixes https://github.com/smartdevicelink/generic_hmi/issues/523

Testing Plan

• [x] I have verified that I have not introduced new warnings in this PR (or explain why below)
• [x] I have tested this PR against Core and verified behavior (if applicable, if not applicable, explain why below).

Core Tests

Perform steps described in issue

Core version / branch / commit hash / module tested against: release/8.2.0 branch

Summary

Only send WARNINGS response for missing alert images if normal result is SUCCESS

Changelog

Bug Fixes

• Only send WARNINGS response for missing alert images if normal result is SUCCESS

CLA

• [x] I have signed the CLA