style(3p/nix): Final act in the brace-wrapping saga

This last change set was generated by a full clang-tidy run (including
compilation):

    clang-tidy -p ~/projects/nix-build/ \
      -checks=-*,readability-braces-around-statements -fix src/*/*.cc

Actually running clang-tidy requires some massaging to make it play
nice with Nix + meson, I'll be adding a wrapper or something for that soon.

third_party/nix/src/libexpr/value-to-json.cc

@@ -58,8 +58,9 @@ void printValueAsJSON(EvalState& state, bool strict, Value& v,
           auto placeholder(obj.placeholder(j));
           printValueAsJSON(state, strict, *a.value, placeholder, context);
         }
-      } else
+      } else {
         printValueAsJSON(state, strict, *i->value, out, context);
+      }
       break;
     }