Return isNegative() and not false, if CondIsWithin is invalid

[TenFont]

Description

This PR fixes the fact that CondIsWithin always returns false if:

• either of the two locations in is within %location% and %location is null, or if both are in separate worlds
• if the "container" is null in is within %entity/chunk/world/block%

Now, it takes into account whether the condition is negated, and returns true or false appropriately.

What was the issue?

Say I have a guard clause like so:

if player is not within {_loc1} and {_loc2}:
  send "&cThe region specified is invalid."
  stop
# do something

If the condition fails, one would assume that the player is within the two locations. However, this precondition is violated if either of the two locations are not set. As the condition is doomed to always fail if the locations are null (regardless of negation), the following code will still run. This PR fixes this.

---

Target Minecraft Versions: any
Requirements: none
Related Issues: none

[sovdeeth]

I'm not sure if I like this approach. A player not being in a region implies the region exists to begin with. I think the current behavior matches better with established convention of NaN always returning false when compared to other numbers. That said, I'm not sure what behavior is most common within Skript's conditions.

[TenFont]

I'm not sure if I like this approach. A player not being in a region implies the region exists to begin with. I think the current behavior matches better with established convention of NaN always returning false when compared to other numbers. That said, I'm not sure what behavior is most common within Skript's conditions.

CondContains returns isNegated() if the container is not set, not false. Current behaviour of CondIsWithin is inconsistent.

[sovdeeth]

Yeah looking at SimpleExpression#check() it does seem precedent to return negated if null valued.
I think that's probably a poor decision in most cases but it's better to be consistent, so ignore my concerns for this PR.