A very simple solution to this problem is to put a file named “PerforceBuild.txt” in your Engine/Build directory. Then when the editor opens without the launcher, it won’t open the launcher. No source patch needed.
It may have some other, subtle effects but it’s probably fine. Just remove it for production.
For reference, this is the condition you are changing to yes:
FEngineBuildSettings::IsPerforceBuild()