tl-parser build step doesn't fail if there is a parse error in .tl file

[abacabadabacaba]

If I modify a *.tl file and the new file has a parse error, I expect the build step that converts it into *.tlo to fail. Instead, it is treated as successful, and it is the next step that fails (with an unhelpful message like Config file scheme/ton_api.tlo is empty, even though the file actually doesn't exist). It would be easier to work with the code if build scripts detected build failures correctly.