* gdk/gdkimage.c: (gdk_image_get):
Deal with the possibility that XGetImage() might return NULL.
Allocate the GdkImagePrivate structure only after XGetImage()
succeeds in order not to dereference a NULL ximage pointer. This
prevents a core dump when XGetImage() fails - which is unlikely,
but can happen due to race conditions accessing the geometries of
drawables. An x error will still be triggered, but the gdk image
wrapper at least wont seg fault.