extmod/uasyncio: Truncate negative sleeps to 0.

Otherwise a task that continuously awaits on a large negative sleep can
monopolise the scheduler (because its wake time is always less than
everything else in the pairing heap).

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/tests/extmod/uasyncio_fair.py b/tests/extmod/uasyncio_fair.py
index 9b04454bc1..e0ee811a9b 100644
--- a/tests/extmod/uasyncio_fair.py
+++ b/tests/extmod/uasyncio_fair.py
@@ -22,6 +22,7 @@ async def main():
     t1 = asyncio.create_task(task(1, -0.01))
     t2 = asyncio.create_task(task(2, 0.1))
     t3 = asyncio.create_task(task(3, 0.2))
+    t3 = asyncio.create_task(task(4, -100))
     await asyncio.sleep(0.5)
     t1.cancel()
     t2.cancel()