Fix QColorTransform memory leak

Introduced recently when the smart-pointer was made manual.

Change-Id: I29a041631e94a8e131dd29dae32975d68b386e00
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/gui/painting/qcolorspace.cpp

@@ -364,6 +364,7 @@ QColorTransform QColorSpacePrivate::transformationToColorSpace(const QColorSpace
     QColorTransform combined;
     auto ptr = new QColorTransformPrivate;
     combined.d = ptr;
+    combined.d->ref.ref();
     ptr->colorSpaceIn = this;
     ptr->colorSpaceOut = out;
     ptr->colorMatrix = out->toXyz.inverted() * toXyz;