Add assert! for image dims in bilateral_filter

[cospectrum]

Someone can create an image with dim > i32::MAX as u32 and dim as i32 will be negative.

[cospectrum]

I checked, there is an assert!(min <= max) in i32::clamp below. But you can still merge, so that readers will understand that this is important.

[cospectrum]

Someday I will write proptests, but not today!

[theotherphil]

Thanks