Can't cook a subsequent release when the project uses World Partition.

A licensee reported getting errors when cooking a subsequent release. The bug is a side effect of CL44557776 which changed the behavior when dealing with generated packages in UCookOnTheFlyServer::GetAllPackageFilenamesFromAssetRegistry.

1. create a new project
2. add a WorldPartition level
3. Create a release package
   1. Set -createreleaseversionroot= and -createreleaseversion= in the BuildCookRun argument

   2. RunUAT.bat BuildCookRun -project=D:/P4/Release57/Custom57/Custom57.uproject -unrealexe=D:\P4\Release57\Engine\Binaries\Win64\UnrealEditor-Cmd.exe -nosign -nocodesign -config=Shipping -platform=Win64 -distribution  -createreleaseversionroot=D:/P4/Release57/Custom57/Releases -basedonreleaseversionroot=D:/P4/Release57/Custom57/Releases -createreleaseversion=1.0 -noP4 -cook -unversionedcookedcontent -skipstage -skippak 
      

4. Change the WP level: Add a new instance or move something
5. Create a new release
   1. Add -originalreleaseversion= and -basedonreleaseversion= to the BuildCookRun argument
   2. Bump -createreleaseversion

   3. RunUAT.bat BuildCookRun -project=D:/P4/Release57/Custom57/Custom57.uproject -unrealexe=D:\P4\Release57\Engine\Binaries\Win64\UnrealEditor-Cmd.exe -nosign -nocodesign -config=Shipping -platform=Win64 -distribution  -createreleaseversionroot=D:/P4/Release57/Custom57/Releases -basedonreleaseversionroot=D:/P4/Release57/Custom57/Releases -originalreleaseversion=1.0 -createreleaseversion=1.4 -basedonreleaseversion=1.0 -noP4 -cook -unversionedcookedcontent -skipstage -skippak 

The sample commands only cook to speed thing up remove -skipstage -skippak_and add _-pak -stage -package to get a StagedBuild to test the releases.