Auto-search on too many addresses hangs entire system

[YoshiRulz]

Basically #1155 but for the search part of RAM Search. I'm thinking disable the button when there are >=65536 addresses—it's not like this removes functionality for those with powerful machines, the manual search button will still be available.

see also #199

[Meerkov]

Instead, what if you do it based on time? e.g. if it takes 15 seconds and still hasn't finished processing the frame, then cancel the auto search and pause the emu with a warning?

I've accidentally hanged my RAM search many times, and I just learned to suffer with it. But an escape hatch like this would be OK.