style(3p/nix): Add braces around single-line for-loops r/772

These were not caught by the previous clang-tidy invocation, but were
instead sorted out using amber[0] as such:

    ambr --regex 'for (\(.+\))\s([a-z].*;)' 'for $1 { $2 }'

[0]: https://github.com/dalance/amber

1 files changed, 3 insertions, 1 deletions

diff --git a/third_party/nix/src/libstore/nar-accessor.cc b/third_party/nix/src/libstore/nar-accessor.cc
index 0214561da456..8a57179ab34a 100644
--- a/third_party/nix/src/libstore/nar-accessor.cc
+++ b/third_party/nix/src/libstore/nar-accessor.cc
@@ -178,7 +178,9 @@ struct NarAccessor : public FSAccessor {
                   path);
 
     StringSet res;
-    for (auto& child : i.children) res.insert(child.first);
+    for (auto& child : i.children) {
+      res.insert(child.first);
+    }
 
     return res;
   }