[3.14] gh-135698: Fix Cross-interpreter Queue.full() With Negative/Default max_size (gh-135775)

We weren't handling non-positive maxsize values (including the default) properly
in Queue.full().  This change fixes that and adjusts an associated assert.

(cherry picked from commit c5ea8e8e8, AKA gh-135724)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>