qoi: fix reports from quality scanner

struct QoiHeader is initialized to invalid values prior use,
it’s good to detect situations when we read incomplete data.
Add include in scanlineconverter.cpp so it can be used without
change in kf5 branch.

src/imageformats/scanlineconverter.cpp

@@ -5,6 +5,7 @@
 */
 
 #include "scanlineconverter_p.h"
+#include <cstring>
 
 ScanLineConverter::ScanLineConverter(const QImage::Format &targetFormat)
     : _targetFormat(targetFormat)