Fix Circleci build failure: Add != operator for Marching Cubes Vertex struct

Summary: Fix Circleci error: https://app.circleci.com/pipelines/github/facebookresearch/pytorch3d/1066/workflows/94df137b-4882-4959-8fe4-738af447db23/jobs/56560.

Reviewed By: kjchalup

Differential Revision: D40185409

fbshipit-source-id: 7121b0cae66bd60f718df2a5d9ef5d2ac3bc658c

Author: Jiali Duan

pytorch3d/csrc/marching_cubes/marching_cubes_cpu.cpp

@@ -86,8 +86,8 @@ std::tuple<at::Tensor, at::Tensor> MarchingCubesCpu(
             }
             tri.clear();
             ps.clear();
-          }
-        } // endif
+          } // endif
+        } // endfor edge enumeration
       } // endfor x
     } // endfor y
   } // endfor z

pytorch3d/csrc/marching_cubes/marching_cubes_utils.h

@@ -310,13 +310,16 @@ struct Vertex {
   Vertex operator+(const Vertex& xyz) const {
     return Vertex(x + xyz.x, y + xyz.y, z + xyz.z);
   }
-  // The == operator overrides is used for checking degenerate triangles
+  // The =/!= operator overrides is used for checking degenerate triangles
   bool operator==(const Vertex& xyz) const {
-    if (std::abs(x - xyz.x) < EPS && std::abs(y - xyz.y) < EPS &&
-        std::abs(z - xyz.z) < EPS) {
-      return true;
-    }
-    return false;
+    return (
+        std::abs(x - xyz.x) < EPS && std::abs(y - xyz.y) < EPS &&
+        std::abs(z - xyz.z) < EPS);
+  }
+  bool operator!=(const Vertex& xyz) const {
+    return (
+        std::abs(x - xyz.x) >= EPS || std::abs(y - xyz.y) >= EPS ||
+        std::abs(z - xyz.z) >= EPS);
   }
   // vertex position
   float x, y, z;