ext: Replace Queue.Empty with queue.empty
ext: Replace Queue.Empty with queue.empty

Queue.Empty is not an exception in python3
(Queue has been renamed to queue)

Change-Id: I82555d96608094fa47990f888fd11663379547bc
Signed-off-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40135
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5