[CP-SAT] fix diffn cut; more tests

Author: lperron

Diff for: ortools/sat/diffn_cuts.cc

@@ -335,8 +335,8 @@ CutGenerator CreateNoOverlap2dEnergyCutGenerator(
     rectangles.reserve(num_rectangles);
     for (const auto& component :
          helper->connected_components().AsVectorOfSpan()) {
-      rectangles.clear();
       for (const int rect : component) {
+        rectangles.clear();
         if (helper->IsAbsent(rect)) continue;
         // We do not consider rectangles controlled by 2 different unassigned
         // enforcement literals.

Diff for: ortools/sat/python/cp_model_test.py

@@ -1940,6 +1940,7 @@ def test_small_series(self) -> None:
         model = cp_model.CpModel()
         x = model.new_bool_var("foo")
         y = model.new_bool_var("bar")
+        z = model.new_bool_var("baz")
 
         s1 = pd.Series([x, y], index=[1, 2])
         self.assertEqual(str(s1.sum()), "(foo + bar)")
@@ -1951,6 +1952,11 @@ def test_small_series(self) -> None:
         s4 = pd.Series([1], index=[1])
         self.assertIs(s3.dot(s4), x)
 
+        s5 = pd.Series([x, y, z], index=[1, 2, 3])
+        self.assertEqual(str(s5.sum()), "(foo + bar + baz)")
+        s6 = pd.Series([1, -2, 1], index=[1, 2, 3])
+        self.assertEqual(str(s5.dot(s6)), "(foo + (-2 * bar) + baz)")
+
     def test_issue4376_sat_model(self) -> None:
         letters: str = "BCFLMRT"