System information (version)

• OpenCV => 4.5.4-dev
• Operating System / Platform => Windows 64 Bit
• Compiler => precompiled from opencv-contrib-python-headless 4.5.4.58

Detailed description

Issue encountered in python: opencv/opencv-python#575
cvtColor should be able to convert a single pixel's color as it does in version 4.5.3

Steps to reproduce

import cv2
import numpy as np

pixel = np.uint8([[[40, 50, 200]]])
new_pixel = cv2.cvtColor(pixel, cv2.COLOR_RGB2BGR)
print(new_pixel)

with OpenCV 4.5.3, this runs successfully. With OpenCV 4.5.4-dev, I get the following error:
OpenCV(4.5.4-dev) D:\a\opencv-python\opencv-python\opencv\modules\core\src\matrix.cpp:466: error: (-215:Assertion failed) _step >= minstep in function 'cv::Mat::Mat'

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  forum.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc