fix(library/unifier): bug in the new next_delta_unfold_case_split

src/library/unifier.cpp

@@ -1204,13 +1204,17 @@ struct unifier_fn {
             if (dcs.first) {
                 constraints cnstrs = dcs.second.to_list();
                 return process_constraints(cnstrs, mk_composite1(cs.get_jst(), mk_assumption_justification(cs.m_assumption_idx)));
+            } else {
+                set_conflict(j);
+                return false;
             }
-        }
+        } else {
             // update conflict
             update_conflict(mk_composite1(*m_conflict, cs.m_failed_justifications));
             pop_case_split();
             return false;
         }
+    }
 
     /**
         \brief Solve constraints of the form (f a_1 ... a_n) =?= (f b_1 ... b_n) where f can be expanded.