Add a property hint to fix crash when setting max convex hulls below 0

[Calinou]

Generating less than 1 convex hull is not valid anyway.

I assume generating more than 100 convex shapes for a single mesh would be ill-advised, so I've set the maximum value to that.

[akien-mga]

Looks good, but I would also add an ERR_FAIL_COND where it's used to make sure invalid .import files don't trigger a crash.

[akien-mga]

Looks good, but I would also add an ERR_FAIL_COND where it's used to make sure invalid .import files don't trigger a crash.

Amended the commit, added a MAX(1, ...) instead as I'm not sure it would handle an early return gracefully, and it's an edge case where the value would be invalid in the .import file.

[akien-mga]

Thanks!