Can not dump an annotation for task with several jobs.

[azhavoro]

Seldom it is impossible to dump annotation for task with several jobs. As a rule annotation consists of a grouped bbox with several points. Task details:

assignee: null
bug_tracker: "..."
created_date: "..."
frame_filter: ""
id: ...
image_quality: 50
labels: [{id: 9313, name: "5", attributes: []}, {id: 9312, name: "4", attributes: []},…]
mode: "annotation"
name: "..."
overlap: 0
owner: ...
segment_size: 1000
segments: […]
size: 4000
start_frame: 0
status: "annotation"
stop_frame: 0
updated_date: "..."
url: "..."
z_order: false

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/rq/worker.py", line 812, in perform_job
    rv = job.perform()
  File "/usr/local/lib/python3.5/dist-packages/rq/job.py", line 588, in perform
    self._result = self._execute()
  File "/usr/local/lib/python3.5/dist-packages/rq/job.py", line 594, in _execute
    return self.func(*self.args, **self.kwargs)
  File "/home/django/cvat/apps/engine/annotation.py", line 121, in dump_task_data
    annotation.dump(file_path, scheme, host, query_params)
  File "/home/django/cvat/apps/engine/annotation.py", line 1306, in dump
    for shape in data_manager.to_shapes(db_task.size):
  File "/home/django/cvat/apps/engine/annotation.py", line 796, in to_shapes
    return shapes + tracks.to_shapes(end_frame)
  File "/home/django/cvat/apps/engine/annotation.py", line 992, in to_shapes
    for shape in TrackManager.get_interpolated_shapes(track, 0, end_frame):
  File "/home/django/cvat/apps/engine/annotation.py", line 1118, in get_interpolated_shapes
    assert shape["frame"] > curr_frame

For now scenario that leads to the issue is not clear.