allow client to remove created tasks with PID 0

Fixes #7357

If a container is restored from a checkpoint that has a configuration
error, the task for the restored container is created, but fails to
start and is left in the state CREATED with a PID of 0. Before this
change, the only way to remove this task was to find the PID of the shim
monitoring the task and kill that process. Now, ctr t rm <task> will
work on tasks that result in the CREATED state with PID 0.

Signed-off-by: Gavin Inglis <giinglis@amazon.com>

task.go

@@ -311,6 +311,11 @@ func (t *task) Delete(ctx context.Context, opts ...ProcessDeleteOpts) (*ExitStat
 			// On windows Created is akin to Stopped
 			break
 		}
+		if t.pid == 0 {
+			// allow for deletion of created tasks with PID 0
+			// https://github.com/containerd/containerd/issues/7357
+			break
+		}
 		fallthrough
 	default:
 		return nil, fmt.Errorf("task must be stopped before deletion: %s: %w", status.Status, errdefs.ErrFailedPrecondition)