Fix change propagation in simplify_byte_extract

f936554 updated the interface of simplify_if, but in one case
failed to propagate changes. This results in missed simplification, and
thus substantially more complicated formulas.

Author: tautschnig

src/util/simplify_expr.cpp

@@ -1975,7 +1975,7 @@ simplify_exprt::simplify_byte_extract(const byte_extract_exprt &expr)
       simplify_byte_extract(to_byte_extract_expr(if_expr.true_case()));
     if_expr.false_case() =
       simplify_byte_extract(to_byte_extract_expr(if_expr.false_case()));
-    return simplify_if(if_expr);
+    return changed(simplify_if(if_expr));
   }
 
   const auto el_size = pointer_offset_bits(expr.type(), ns);