fix miscast of a pointer in SetWindowLongPtr
fix miscast of a pointer in SetWindowLongPtr

GCC 4.4.0 complains error: cast from pointer to integer of different size
Fixes #584678.

mapmapteam/gst-plugins-gl,ystreet/gst-plugins-gl,ystreet/gst-plugins-gl,ystreet/gst-plugins-gl,mapmapteam/gst-plugins-gl,mapmapteam/gst-plugins-gl