System information (version)

• OpenCV =>4.4.0 and 4.5.0
• Operating System / Platform => Windows 10 and Ubuntu 20.04

Detailed description

I'm trying to use a mobilenet v3 large model. I have got an error when I try to instantiate a new dnn_DetectionModel object.

cv2.error: OpenCV(4.4.0) C:\OpenCV\4.4.0\opencv\modules\dnn\src\dnn.cpp:3466: error: (-215:Assertion failed) total(os[i]) > 0 in function 'cv::dnn::dnn4_v20200609::Net::Impl::getLayerShapesRecursively'

I saw that last version of opencv 4.x.x support mobilenet v3

Steps to reproduce

net = cv2.dnn_DetectionModel("....pb")

Issue submission checklist

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