Fix indentation level.

[reu]

Just a very small tweak that I found by accident while skimming the code.

By the way, if you wish I could apply Rust Format defaults to the project as whole. I see that there are some places that we need to add Rust Format ignore directives (such as in some tests/benchmarks mainly), but for most of the code it is very convenient to have automatic formatting. Anyway, just let me know if you would consider a merge for a PR like that.