Saving a QImage to BMP will cause it to detach

Location: src/gui/image/qbmphandler.cpp, function qt_write_dib, lines 592, 609 and 619

Because the argument 'QImage image' is non-const, the calls to QImage::scanLine on the aforementioned lines will cause an unnecessary detach.

Solution (as used in other image format handlers): change

  image.scanLine(y)

into

  static_cast<const QImage&>(image).scanLine(y)

and make pointer p declared on line 604 const.