If num_find is zero attempt to explore all possible states

[nmeum]

I wanted to explore all possible paths (i.e. run explore() until the active stash is empty). The only(?) way to do that right now seems to be to set num_find in the explore() invocation to a very high number, for example:

simgr.explore(num_find=999999999, find=…)

However, this does seem a bit hacky. Therefore, I propose adding a special value for num_find which causes all paths to be explored. This is implemented in this PR via num_find=0.

[ltfish]

Have you ever tried passing in num_find=None, or just not passing num_find at all?

[ltfish]

Uh I think this is a leftover problem from the Python 2 to 3 conversion...

The actual check should probably be return self.num_find is None and not simgr.stashes["active"] or len(simgr.stashes[self.find_stash]) >= self.num_find.

[nmeum]

Not passing num_find does not work as it defaults to 1. Using None does not work because—as you pointed out—there is no explicit handling for num_find is None. However, I can updated my PR to instead explore all paths if num_find is None instead of 0.

[ltfish]

@rhelmot As the magician designing amazing interfaces, what do you think?