Don't check parent's persistTaskBounds unless child is UNDEFINED.

When Task gets an onConfigurationChanged call with a requested
overriding configuration, it checks for itself and its parent's ability
to see if persisting task bounds is possible or not. This was done for
the case of freeform window support, where if the current window is
undefined (persistBounds = false), it will then check for the parents
(could be clamhshell, which persistBounds = true, or tablet, which
persistBounds = false).

However, there exists a case where this does not work well, which is
when freeform window (inheriting from a freeform display) enters PIP,
pinned windowing mode. We have already provided new PIP bounds, but
since undefined window are not persistable and neither is PIP, but PIP's
parent (the freeform display) is, it will end up setting the new bounds
back to mLastNonFullscreenBounds, which is the freeform bounds. We then
end up losing the new PIP bounds.

Bug: 152911516
Test: On a freeform display, open an activity and enter PIP - PIP
activity now has the correct bounds

Change-Id: If73523ba1c54274eb5be4af5b967c6fef2993898