CheatSearchTab: Check Core state instead of checking a memory pointer.

[CrossVR]

Fixes issue 8714.

[AdmiralCurtiss]

Should be changed a few lines down in FilterCheatSearchResults() too.

Frankly I'm more curious why the memory pointer doesn't get null'd after emulation ends but this probably works.

[CrossVR]

@AdmiralCurtiss I think that's the kind of behaviour no one should rely on, especially not for something as important as state checking.

[phire]

I think you actually want Core::IsRunning()

Otherwise you will be unable to use Cheat Search while dolphin is paused, which is kind of necessary at times.

[CrossVR]

@phire Core::IsRunningAndStarted() checks if the CPU thread has started, it is unrelated to whether it is paused.