Add missing member initializers of string_constraintst-typed value

add_axioms_for_char_at, add_axioms_for_is_empty, add_axioms_from_char only
initialized one of the three vectors.

Author: tautschnig

src/solvers/refinement/string_constraint_generator_main.cpp

@@ -576,7 +576,7 @@ std::pair<exprt, string_constraintst> add_axioms_for_char_at(
   array_string_exprt str = get_string_expr(array_pool, f.arguments()[0]);
   symbol_exprt char_sym = fresh_symbol("char", str.type().subtype());
   const exprt constraint = equal_exprt(char_sym, str[f.arguments()[1]]);
-  return {char_sym, {{constraint}}};
+  return {char_sym, {{constraint}, {}, {}}};
 }
 
 exprt minimum(const exprt &a, const exprt &b)

src/solvers/refinement/string_constraint_generator_testing.cpp

@@ -139,7 +139,7 @@ std::pair<exprt, string_constraintst> add_axioms_for_is_empty(
   std::vector<exprt> constraints;
   constraints.push_back(implies_exprt(is_empty, length_eq(s0, 0)));
   constraints.push_back(implies_exprt(length_eq(s0, 0), is_empty));
-  return {typecast_exprt(is_empty, f.type()), {constraints}};
+  return {typecast_exprt(is_empty, f.type()), {constraints, {}, {}}};
 }
 
 /// Test if the target is a suffix of the string

src/solvers/refinement/string_constraint_generator_valueof.cpp

@@ -332,7 +332,7 @@ std::pair<exprt, string_constraintst> add_axioms_from_char(
   const exprt &c)
 {
   const and_exprt lemma(equal_exprt(res[0], c), length_eq(res, 1));
-  return {from_integer(0, get_return_code_type()), {{lemma}}};
+  return {from_integer(0, get_return_code_type()), {{lemma}, {}, {}}};
 }
 
 /// Add axioms making the return value true if the given string is a correct