QDataStream::skipRawData no longer works with negative values

In Qt 5.9 it was possible to call QDataStream::skipRawData with a negative offset to move backwards through a file, but in Qt 5.12 and 5.15 it gives an error "QIODevice::skip (QBuffer): Called with maxSize < 0" instead.

It looks like internally it was changed (for non-sequential devices) to use QIODevice::skip() instead of seek(), which doesn't allow negative values.