Despite the QImage::scanLine doc only warning about byte order issues
for 32-bpp formats[0] the same warning seems to apply to 16BPP formats
like QImage::Format_RGB555 as well.
[0]: https://doc.qt.io/qt-6/qimage.html#scanLine
Q_LITTLE_ENDIAN was used incorrectly, it should have been
"#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN"
Use qFromBigEndian since it is more explicit.
Fixes 6d5e61f0b0