Fix invalid memory access in wechat_qrcode byte segment decoding

[determ1ne]

A malicious crafted image will crash the wechat_qrcode module by invalid memory access.

Sample image:

In DecodedBitStreamParser::decodeByteSegment, an attacker can build a qr code with a byte segment, in which the bits count is larger than actually available bits. Code in line 203 will try to read from an invalid memory region and crash the program. An additional sanity check on count should be added.

opencv_contrib/modules/wechat_qrcode/src/zxing/qrcode/decoder/decoded_bit_stream_parser.cpp

Lines 197 to 208 in 960b3f6

	// try to repair count data if count data is invalid
	if (count * 8 > available) {
	count = (available + 7 / 8);
	}
	ArrayRef<char> bytes_(count);
	char* readBytes = &(*bytes_)[0];
	for (int i = 0; i < count; i++) {
	// readBytes[i] = (char) bits.readBits(8);
	int readBits = available < 8 ? available : 8;
	readBytes[i] = (char)bits.readBits(readBits, err_handler);
	}

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• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[dddzg]

I am shocked that the community could find this detailed bug with a sample image. Thanks a lot. This PR could be contained with #3480 .

[WanliZhong]

Thanks for contribution! This bug was fixed by another PR #3480