Iterative Cook does not only cook new content from Unreal Frontend

Using iterative cooking should only cause new or changed content to be cooked but in the Unreal Frontend, content is cooked every time, despite nothing being added or edited.

Logs from two subsequent cooks are attached. Note that there are less cook messages in the second, but as there were no changes made, there should be none.

This was discovered while testing https://jira.it.epicgames.net/browse/UEQATC-1022

Regression?: Yes
This did not occur in 4.19.2

1. Create any BP project in the binary version of the editor
2. Close the project once all shaders compile
3. Open UnrealFrontend from the binary install location of the engine under 4.20\Engine\Binaries\Win64
4. Create a new custom launch profile by clicking on + symbol
5. Under Project Browse to and select your project
6. Leave Build unchecked since this is a binary build
7. Change Cook to By the Book
   1. Check WindowsNoEditor
   2. Check Iterative Cooking
   3. Uncheck Save Packages without versions
8. Do not Package
9. Make Deploy Copy to Device and check your local machine
10. Make launch Do Not Launch
11. Click the back button
12. Run the custom profile
13. Save the log
14. Run the custom profile again
15. Compare Cook section of the log to the first one

Result: Some assets are cooked again even with no changes made.

Expected: No assets are cooked since no changes were made.