Excessive frame requests in full-length benchmark

[YomikoR]

Results from brand new git master with default options:

2024-03-01 10:31:26.215: concurrent.futures: ERROR: exception calling callback for <Future at 0x7f41d4525390 state=finished raised Error>
Traceback (most recent call last):
  File "/usr/lib/python3.11/concurrent/futures/_base.py", line 340, in _invoke_callbacks
    callback(self)
  File "/home/***/env/vs-env/lib/python3.11/site-packages/vspreview/toolbars/benchmark/toolbar.py", line 198, in _request_next_frame_unsequenced
    future.result()
  File "/usr/lib/python3.11/concurrent/futures/_base.py", line 449, in result
    return self.__get_result()
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/concurrent/futures/_base.py", line 401, in __get_result
    raise self._exception
vapoursynth.Error: Invalid frame number 2000 requested, clip only has 2000 frames