[REG 5.15 -> 6.0] QCborValue::fromCbor allocates 2 GiB for 8 B input

1. Build the attached project.
2. Run it on the attached input:

   ./report input.cbor
   

3. Watch the value of "newSize" in line 1583 of qcborvalue.cpp:

           data.resize(newSize);
   

   Use a breakpoint, a qDebug() or whatever you prefer.
   It will try resizing the QByteArray to 2147483639.

Allocating 2 GiB of memory doesn't seem appropriate for 8 bytes of input.

This is a regression from Qt 5.15. There, the function will return -1 before:

        if (newSize > MaxByteArraySize)
            return -1;