convertARGBToRGBA64PM_avx2 crashes on big images

==13256== Invalid read of size 32
==13256== at 0x4928FB4: _mm256_loadu_si256 (avxintrin.h:921)
==13256== by 0x4928FB4: void convertARGBToRGBA64PM_avx2<false>(QRgba64*, unsigned int const*, long long) (qdrawhelper_avx2.cpp:1120)
==13256== by 0x492C795: fetchARGB32ToRGBA64PM_avx2(QRgba64*, unsigned char const*, int, int, QVector<unsigned int> const*, QDitherInfo*) (qdrawhelper_avx2.cpp:1214)
==13256== by 0x4B5530A: destFetch64(QRgba64*, QRasterBuffer*, int, int, int) (qdrawhelper.cpp:1705)
==13256== by 0x4B5FA2A: blend_untransformed_generic_rgb64(int, QT_FT_Span_ const*, void*) (qdrawhelper.cpp:4800)
==13256== by 0x4B6A6A7: qBlendTexture(int, QT_FT_Span_ const*, void*) (qdrawhelper.cpp:5320)
==13256== by 0x4B903A9: fillRect_normalized(QRect const&, QSpanData*, QRasterPaintEnginePrivate*) (qpaintengine_raster.cpp:1564)
==13256== by 0x4B94E77: QRasterPaintEngine::drawImage(QPointF const&, QImage const&) (qpaintengine_raster.cpp:2273)
==13256== by 0x4BB5208: QPainter::drawImage(QPointF const&, QImage const&) (qpainter.cpp:5400)
==13256== by 0x10912A: main (in /home/tsdgeos/borrame/borrame)