bpo-30595: Fix multiprocessing.Queue.get(timeout) (#2027)

multiprocessing.Queue.get() with a timeout now polls its reader in
non-blocking mode if it succeeded to aquire the lock but the acquire
took longer than the timeout.

Co-Authored-By: Grzegorz Grzywacz <grzgrzgrz3@gmail.com>

Lib/multiprocessing/queues.py

@@ -101,7 +101,7 @@ class Queue(object):
             try:
                 if block:
                     timeout = deadline - time.time()
-                    if timeout < 0 or not self._poll(timeout):
+                    if not self._poll(timeout):
                         raise Empty
                 elif not self._poll():
                     raise Empty