Fix invalid memory access in vector insert method

The stl_bind.h wrapper for `Vector.insert` neglected to do a bounds
check.

include/pybind11/stl_bind.h

@@ -145,6 +145,8 @@ void vector_modifiers(enable_if_t<std::is_copy_constructible<typename Vector::va
 
     cl.def("insert",
         [](Vector &v, SizeType i, const T &x) {
+            if (i > v.size())
+                throw index_error();
             v.insert(v.begin() + (DiffType) i, x);
         },
         arg("i") , arg("x"),