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/attr-set.cc

@@ -10,8 +10,9 @@ namespace nix {
    capacity. The space is implicitly reserved after the Bindings
    structure. */
 Bindings* EvalState::allocBindings(size_t capacity) {
-  if (capacity > std::numeric_limits<Bindings::size_t>::max())
+  if (capacity > std::numeric_limits<Bindings::size_t>::max()) {
     throw Error("attribute set of size %d is too big", capacity);
+  }
   return new (allocBytes(sizeof(Bindings) + sizeof(Attr) * capacity))
       Bindings((Bindings::size_t)capacity);
 }