QRDecoder: return some content even in the presence of a checksum error

This is related to zxing-cpp#828. As an example, with this change, the first image
in zxing-cpp#454 gets decoded as
    "httPs*//ímbizurl.cn/S/fPwhXQqeH"
instead of an empty string, while the correct version is
    "https://mmbizurl.cn/s/fPwhXQqeH"

core/src/qrcode/QRDecoder.cpp

@@ -351,19 +351,23 @@ DecoderResult Decode(const BitMatrix& bits)
 	auto resultIterator = resultBytes.begin();
 
 	// Error-correct and copy data blocks together into a stream of bytes
+	Error error;
 	for (auto& dataBlock : dataBlocks)
 	{
 		ByteArray& codewordBytes = dataBlock.codewords();
 		int numDataCodewords = dataBlock.numDataCodewords();
 
 		if (!CorrectErrors(codewordBytes, numDataCodewords))
-			return ChecksumError();
+			error = ChecksumError();
 
 		resultIterator = std::copy_n(codewordBytes.begin(), numDataCodewords, resultIterator);
 	}
 
 	// Decode the contents of that stream of bytes
-	return DecodeBitStream(std::move(resultBytes), version, formatInfo.ecLevel).setIsMirrored(formatInfo.isMirrored);
+	auto ret = DecodeBitStream(std::move(resultBytes), version, formatInfo.ecLevel).setIsMirrored(formatInfo.isMirrored);
+	if (error)
+		ret.setError(error);
+	return ret;
 }
 
 } // namespace ZXing::QRCode

test/unit/qrcode/MQRDecoderTest.cpp

@@ -96,7 +96,7 @@ TEST(MQRDecoderTest, MQRCodeM1Error4Bits)
 										  88, false);
 	const auto result = Decode(bitMatrix);
 	EXPECT_EQ(Error::Checksum, result.error());
-	EXPECT_TRUE(result.text().empty());
+	EXPECT_EQ(result.text(), L"6350");
 }
 
 TEST(MQRDecoderTest, MQRCodeM4)

test/unit/qrcode/RMQRDecoderTest.cpp

@@ -46,8 +46,8 @@ TEST(RMQRDecoderTest, RMQRCodeR7x43MError6Bits)
 
 	const auto result = Decode(bitMatrix);
 	EXPECT_EQ(Error::Checksum, result.error());
-	EXPECT_TRUE(result.text().empty());
-	EXPECT_TRUE(result.content().text(TextMode::Plain).empty());
+	EXPECT_EQ(result.text(), L"LSZ2EFJ");
+	EXPECT_EQ(result.content().text(TextMode::Plain), "LSZ2EFJ");
 }
 
 TEST(RMQRDecoderTest, RMQRCodeR7x139H)