Fix Amstrad/Olivetti internal mice not working by explicitly defining the number of buttons

src/machine/m_amstrad.c

@@ -2410,6 +2410,7 @@ machine_amstrad_init(const machine_t *model, int type)
     if (mouse_type == MOUSE_TYPE_INTERNAL) {
 /* Tell mouse driver about our internal mouse. */
         mouse_reset();
+        mouse_set_buttons(2);
         mouse_set_poll(ms_poll, ams);
     }
 

src/machine/m_xt_olivetti.c

@@ -426,6 +426,7 @@ m24_kbd_init(m24_kbd_t *kbd)
 
     /* Tell mouse driver about our internal mouse. */
     mouse_reset();
+    mouse_set_buttons(2);
     mouse_set_poll(ms_poll, kbd);
 
     keyboard_set_table(scancode_xt);