fix clipboard history crash

[AlexJonker]

The small preview cut right trough emojis if the emoji was perfectly placed causing a panic.

The text I had the issue with:

zlaunch on  main [!] is 📦 v0.4.0 via 🦀 v1.92.0-nightly

When you have this in your history and try to open the clipboard the daemon crashes. This pr fixes that.

this was the crash:

thread 'main' (344750) panicked at src/clipboard/item.rs:47:49:
byte index 30 is not a char boundary; it is inside '📦' (bytes 27..31) of `zlaunch on  main [!] is 📦 v0.4.0 via 🦀 v1.92.0-nightly`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[zortax]

i can merge this for now, but I think it would be better to properly handle overflow in the UI anyway instead of cutting the preview string...