Big resolution images crash the library

[Lymphatus]

I'm trying to process a quite large PNG (7680 × 4320, ~100Mb) but the library seems to not be able to handle it, panicking with thread 'main' panicked at 'attempt to add with overflow' on src/hist.rs:206:34.

The issue is quite easy to reproduce by running the provided example and just setting

let width = 5000;
let height = 5000;

or anything bigger than that. Crashes all the time on my machine.

Additional info:

• imagequant 4.0.2
• macOS 12.5.1 (MacbookPro 2017, Intel chipset)
• Rust 1.63