[Bug]: Dinamic substring of const string compiles but fails

### Detalles de Contacto

Telegram @Sewave

### Versión del compilador

v1.18.1

### ¿Qué ha pasado?

```
CONST STRING_A AS STRING = "abcdef"
DIM x AS UBYTE = 0
PRINT AT 1,0; STRING_A(x TO x)
```
Compiles but execution prints random characters or crashes

### Mensajes de error o warnings del compilador

```shell

```

### Código de Conducta

- [x] I agree to follow this project's Code of Conduct