Fix return value in einsum_path for simple contractions (#3232)

Co-authored-by: KD2YCU <me@kd2ycu.com>
Co-authored-by: Angelos Katharopoulos <a_katharopoulos@apple.com>

Author: 3 people

mlx/einsum.cpp

@@ -800,7 +800,7 @@ std::pair<std::vector<PathNode>, PathInfo> einsum_path_helper(
     max_size = std::max(max_size, term_size(in, dim_map));
   }
 
-  PathInfo path_info;
+  PathInfo path_info{};
 
   // Get the full naive cost
   std::tie(path_info.naive_cost, path_info.naive_scaling) =
@@ -813,6 +813,8 @@ std::pair<std::vector<PathNode>, PathInfo> einsum_path_helper(
     std::iota(positions.begin(), positions.end(), 0);
     path.emplace_back(
         std::move(inputs), std::move(output), std::move(positions));
+    path_info.optimized_cost = path_info.naive_cost;
+    path_info.optimized_scaling = path_info.naive_scaling;
   } else {
     std::tie(path, path_info.optimized_cost, path_info.optimized_scaling) =
         greedy_path(inputs, output, dim_map, path_info.naive_cost, max_size);