Proposed Changes

Hey, small PR after doing some cleanup :)

It's possible to panic on text.justifyText with strings: negative Repeat count when a cell's display width (CJK-aware, via go-runewidth) exceeds maxLength.
The source of the issue is that numSpacesNeeded = maxLength - textLength + spaces goes negative, then is passed to strings.Repeat, which does panic on negative see here)

I've made this fix: early-return the text unchanged when numSpacesNeeded < 0 (consistent with how AlignCenter handles the overflow case), as it seemed the best way to fix.

If you want a small and easy reproducer that you can run:

package main

import "github.com/jedib0t/go-pretty/v6/text"

func main() {
      // "䈢" (U+4222) has display width 2, so the full string's display width is 12, which exceeds maxLength=10 and triggers:
      //   panic: strings: negative Repeat count
      text.AlignJustify.Apply("a 䈢䈢䈢䈢䈢", 10)
}

I also added a small fuzz test: it won't really run as a fuzz test in your CI as far as I can tell, but should allow you to find similar issues in the future if you run it manually. (Doing the CI setup change to run go test -fuzz is outside of the scope of this PR haha)