fix the bug that cannot detect multi qrcode when use_nn_detector is false

[bit1002lst]

A new PR based on the top of 4.x and fix the conflicts
related issus #3343

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[bit1002lst]

I found there is build fail when decode test case [3_close_qrcodes.png].
May I fix this? I cannot find the test image

[bit1002lst]

@AleksandrPanov

[AleksandrPanov]

@bit1002lst, 3_close_qrcodes.png (from opencv_extra):

[bit1002lst]

@AleksandrPanov Hello, I have tested this image and recurrent this error.
But, actually, this error is not caused by this PR, because it still exist in top 4.x versions when use_nn_detector is false.

[AleksandrPanov]

@bit1002lst, you broke tests with use_nn_detector = true by adding duplicate qr corners to answer

fixed by this commit: fixed duplicate corners and style

also added test with multi detect

[AleksandrPanov]

@asmorkalov, could you check PR?

[bit1002lst]

@bit1002lst, you broke tests with use_nn_detector = true by adding duplicate qr corners to answer

fixed by this commit: fixed duplicate corners and style

also added test with multi detect

Thanks for your help