Fix segfault in TimerHandle.when() after cleared

Fixes #469
Closes #475

Co-authored-by: Fantix King <fantix.king@gmail.com>

.gitignore

@@ -34,3 +34,4 @@ uvloop/loop.*.pyd
 /.eggs
 /.venv*
 /wheelhouse
+/uvloop-dev

tests/test_base.py

@@ -860,6 +860,14 @@ def test_loop_call_later_handle_when(self):
         self.assertAlmostEqual(handle.when(), loop_t + delay, places=2)
         handle.cancel()
         self.assertTrue(handle.cancelled())
+        self.assertAlmostEqual(handle.when(), loop_t + delay, places=2)
+
+    def test_loop_call_later_handle_when_after_fired(self):
+        fut = self.loop.create_future()
+        handle = self.loop.call_later(0.05, fut.set_result, None)
+        when = handle.when()
+        self.loop.run_until_complete(fut)
+        self.assertEqual(handle.when(), when)
 
 
 class TestBaseAIO(_TestBase, AIOTestCase):

uvloop/cbhandles.pxd

@@ -32,6 +32,7 @@ cdef class TimerHandle:
         object context
         tuple _debug_info
         object __weakref__
+        object _when
 
     cdef _run(self)
     cdef _cancel(self)

uvloop/cbhandles.pyx

@@ -193,6 +193,7 @@ cdef class TimerHandle:
             loop, <method_t>self._run, self, delay)
 
         self.timer.start()
+        self._when = self.timer.get_when() * 1e-3
 
         # Only add to loop._timers when `self.timer` is successfully created
         loop._timers.add(self)
@@ -309,7 +310,7 @@ cdef class TimerHandle:
         self._cancel()
 
     def when(self):
-        return self.timer.get_when() * 1e-3
+        return self._when
 
 
 cdef format_callback_name(func):