[bugfix] Fix typo following doublon elimination

Following a bugfix for doublon elimination, doublons are now eliminated
in add_clause, and as such, in case no simplification is made, the
clause without doublons should be used (and not init). This was a typo
missed during the refactoring of doublon elimination.

src/core/internal.ml

@@ -768,8 +768,8 @@ module Make
         if history = []
         then (
           (* update order of atoms *)
-          List.iteri (fun i a -> init.atoms.(i) <- a) atoms;
-          init
+          List.iteri (fun i a -> c.atoms.(i) <- a) atoms;
+          c
         )
         else make_clause ?tag:init.tag (fresh_name ()) atoms (History (c :: history))
       in