This commit adapts the behavior of the commonly used pattern of a GC
that draw onto a plain image. In the windows implementation the monitor
specific scaling could lead to issues with this pattern, because during
creation time of an GC/Image combo it was not always clear with which
zoom the final result will be drawn upon. This commit will redraw the
GC on an image handle if a new zoom is requested. The handle for the
old zoom of the image will be kept, but if another operation of the GC
is exeuted it will only be applied on the new handle.