Looking for commit in source fixing landscape crash

When using landscape shaders in Unreal 4.13 (both binary and source), the editor crashes when building the game. This is the error message I get:

Using Unreal 4.14 the build works fine, so the bug seems to have been fixed. Unfortunately we cannot update to 4.14 because we implemented multiple modifications in the engine source, so I want to merge only the fix to this specific problem into our source. I could not find an issue or commit message referring to this problem, so I am having troubles with finding the commit that fixed this issue. Does anybody know what fixed it or have any ideas on how to proceed?

Thanks in advance