Correct offset in eval for insert

Author: romainbrenguier

src/solvers/refinement/string_builtin_function.cpp

@@ -164,7 +164,8 @@ std::vector<mp_integer> string_insertion_builtin_functiont::eval(
   const std::vector<mp_integer> &args_value) const
 {
   PRECONDITION(args_value.size() >= 1 || args_value.size() <= 3);
-  const auto offset = std::max(args_value[0], mp_integer(0));
+  const auto offset = std::min(std::max(args_value[0], mp_integer(0)),
+                               mp_integer(input1_value.size()));
   const auto start = args_value.size() > 1
                      ?std::max(args_value[1], mp_integer(0))
                      :mp_integer(0);