icount was missing from the savestates

When you load a state, icount (*icountptr) would remain whatever it was before loading, messing with the remaining cycles and with the amount of code executed per run() call. This introduced non-determinism and badly influenced usage of savestates while debugging. machine().time() would also return wrong values after that, since it adds remaining cycles.

src/emu/diexec.cpp

@@ -499,6 +499,7 @@ void device_execute_interface::interface_post_start()
 	assert_always(m_icountptr != nullptr, "m_icountptr never initialized!");
 
 	// register for save states
+	device().save_pointer(NAME(m_icountptr), 1);
 	device().save_item(NAME(m_suspend));
 	device().save_item(NAME(m_nextsuspend));
 	device().save_item(NAME(m_eatcycles));