Clarify behavior of `GenericImage::copy_within`

[RunDevelopment]

image/src/images/generic_image.rs

Lines 278 to 298 in 03f097f

	/// Copies all of the pixels from one part of this image to another part of this image.
	///
	/// The destination rectangle of the copy is specified with the top-left corner placed at (x, y).
	///
	/// # Returns
	/// `true` if the copy was successful, `false` if the image could not
	/// be copied due to size constraints.
	fn copy_within(&mut self, source: Rect, x: u32, y: u32) -> bool {
	let Rect {
	x: sx,
	y: sy,
	width,
	height,
	} = source;
	let dx = x;
	let dy = y;
	assert!(sx < self.width() && dx < self.width());
	assert!(sy < self.height() && dy < self.height());
	if self.width() - dx.max(sx) < width || self.height() - dy.max(sy) < height {
	return false;
	}

This method panics when the offset of the source rectangle or target rectangle (given by x and y) are outside the bounds of the image. This panic is not documented and seems unintentional given that copy_within could just return false.

What is the intended behavior here?

If panicking is intended, it should be documented. If not, then it should return false.

---

I git blamed a bit and found the source.