fix rand.Intn painc

[zuiwuchang]

#109

大量的 rand.Intn 調用在傳入非法參數時將引發 painc。但通常這是 rand.Intn 返回 0 而非 painc 可能會使 base64Captcha 庫更容易使用。這份 pull 將對 rand.Intn 的調用替換爲了下述代碼以避免 painc

func randIntn(n int) int {
	if n > 0 {
		return rand.Intn(n)
	}
	return 0
}

[Copilot]

Pull Request Overview

This PR addresses panic issues in the base64Captcha library by replacing direct rand.Intn calls with a safer wrapper function randIntn that prevents panics when negative or zero parameters are passed.

• Introduces a new randIntn function that returns 0 for non-positive inputs instead of panicking
• Replaces all rand.Intn calls throughout the codebase with the safer randIntn function
• Removes unused math/rand imports where appropriate

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
randIntn.go	New helper function that wraps rand.Intn with panic prevention
random_math.go	Updates RandText and randIntRange functions to use safe wrapper
item_digit.go	Updates strikeThrough and randomBrightness functions to use safe wrapper
item_char.go	Updates multiple drawing functions and reorganizes imports
item_audio.go	Updates makeBackgroundSound function to use safe wrapper
fonts.go	Updates randFontFrom function and removes unused import
driver_language.go	Updates generateRandomRune function and removes unused import
driver_digit.go	Updates DrawCaptcha function to use safe wrapper
driver_chinese.go	Updates GenerateIdQuestionAnswer function and removes unused import

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[Copilot]

Pull Request Overview

Copilot reviewed 9 out of 10 changed files in this pull request and generated 4 comments.

---

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[Copilot]

[nitpick] The commented code on line 48 shows inconsistent usage - it adds y to randIntn(y) which could exceed bounds, while the new code would return 0 for invalid parameters. Consider removing this outdated comment or updating it to reflect the current safe behavior.

Suggested change

//y1 := float64(randIntn(y)+y);

[Copilot]

This line still uses the unsafe rand.Intn() directly instead of the safe randIntn() wrapper that was introduced to prevent panics. This should be updated to randIntn(5) for consistency with the rest of the changes.

Suggested change

	multiple := float64(rand.Intn(5)+3) / float64(5)
	multiple := float64(randIntn(5)+3) / float64(5)

[Copilot]

This line still uses the unsafe rand.Intn() directly instead of the safe randIntn() wrapper. This should be updated to randIntn(5) for consistency with the rest of the changes.

Suggested change

	fontSize := rawFontSize/2 + float64(rand.Intn(5))
	fontSize := rawFontSize/2 + float64(randIntn(5))

[Copilot]

This line still uses the unsafe rand.Intn() directly instead of the safe randIntn() wrapper. This should be updated to randIntn(10) for consistency with the rest of the changes.

Suggested change

	snd := reversedSound(a.digitSounds[rand.Intn(10)])
	snd := reversedSound(a.digitSounds[randIntn(10)])