Unnecessary Repeated Calls to self.nes.is_empty()

[silverhadch]

The self.nes.is_empty() check is called multiple times in different methods (e.g., get_save_state_path, get_present_save_states). This could lead to redundant checks.

Cache the result of self.nes.is_empty() in a local variable or within the struct to avoid unnecessary repeated calls.

[Amjad50]

Closed by #13