fixed a off-by-one error in size checking
fixed a off-by-one error in size checking

fixes https://github.com/gphoto/gphoto2/issues/29

gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2