Clean up console errors

[bnmajor]

• We have some console errors Cannot read properties of null (reading 'layers') which probably occurs when switching images. We should probably just guard this so it doesn't happen.
• Possible coupled with the previous, sometimes I see a Cannot read properties of null (reading 'removeEventListener') error when we do document.querySelector(".resize-handle").removeEventListener("mousedown", ...

Originally posted by @manthey in #131 (comment)