BUG: Prevent free'ing uninitialized pointer in DeviceEvents

Author: mdboom

cuda_core/cuda/core/system/_event.pxi

@@ -144,13 +144,15 @@ cdef class DeviceEvents:
             raise TypeError("events must be an EventType, str, or list of EventType or str")
 
         self._device_handle = device_handle
+        self._event_set = 0
         self._event_set = nvml.event_set_create()
         # If this raises, the event needs to be freed and this is handled by
         # this class's __dealloc__ method.
         nvml.device_register_events(self._device_handle, event_bitmask, self._event_set)
 
     def __dealloc__(self):
-        nvml.event_set_free(self._event_set)
+        if self._event_set != 0:
+            nvml.event_set_free(self._event_set)
 
     def wait(self, timeout_ms: int = 0) -> EventData:
         """