Scylla takes a lot of time when listing

Hi,

I was using version 9.7c (don't jump on me to tell me 9.8 is released, I know !) and noticed that when listing a lot of imports (most of them are invalid), the app takes a lot of time.

Same goes when trying to delete/cut a lot of thunks.

So, I though it would be better to add "Disable listing" option to make the app faster in case it faces a lot of wrong pointers.

BTW, 9.8 is doesn't find these invalid pointers, but let's say that one can exploit this to trick 9.8 as well !