Fix CopySpace::is_live

[k-sareen]

This commit fixes the CopySpace::is_live function to check if a to-space object's address is actually below the current page resource cursor. By definition, a to-space object cannot be live if it is beyond the cursor.

[k-sareen]

Ran into this bug when I was using fixed extent semi-spaces. Since we don't zero pages on release, we could have stale data there from the last GC wherein the (dead) object is beyond the cursor but it was forwarded so both !self.is_from_space() and is_forwarded will return true. The fix now makes it clearer that it needs to be mutually exclusive, i.e. we can't have forwarded objects in to-space.

[qinsoon]

Ran into this bug when I was using fixed extent semi-spaces. Since we don't zero pages on release, we could have stale data there from the last GC wherein the (dead) object is beyond the cursor but it was forwarded so both !self.is_from_space() and is_forwarded will return true. The fix now makes it clearer that it needs to be mutually exclusive, i.e. we can't have forwarded objects in to-space.

The function is_live requires an object reference. But in this case, what gets passed to the function is not a valid object reference.