* pyclipper inhomogeneous expanded array solved
For some images, `np.array(offset.Execute(distance))` can result in inhomogeneous part of the detection box list, which cannot be casted into numpy array directly.
* corrected box reshape position
- box reshape was mistakenly done at line 145 which is now correctly done at line 92 of `db_postprocess.py`
- if box is empty then continue
* reverted mistakenly changed line 147
- reverted mistakenly changed `box.array(box)` to `np.array(box)`
* expanded array fix for `det_box_type=quad`
* polygons padding
For `--det_box_type = poly`, pad the detected polygon arrays if they have different shapes to ensure even shapes of polygon arrays
* fix codestyle
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Co-authored-by: Wang Xin <xinwang614@gmail.com>