设置字符集为英文字母时，验证容易报错

[fqw123]

1. 设置英文字符集

chars := "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"

_ = capt.SetRangChars(strings.Split(chars, ""))

capt = captcha.GetCaptcha()

dots, b64, tb64, key, err := capt.Generate()

2. 前端点选结果

{"dot":"110,198,48,88,197,72","key":"c39190357e6e59043729c59a8fa99a71"}

3. 实际点选结果
   {"0":{"Index":0,"Dx":105,"Dy":227,"Size":38,"Width":38,"Height":38,"Text":"N","Angle":330,"Color":"#fcb08e","Color2":"#6e3700"},"1":{"Index":1,"Dx":50,"Dy":111,"Size":31,"Width":31,"Height":31,"Text":"A","Angle":20,"Color":"#60c1ff","Color2":"#6e3700"},"2":{"Index":2,"Dx":193,"Dy":96,"Size":37,"Width":37,"Height":37,"Text":"F","Angle":325,"Color":"#b4fed4","Color2":"#660033"}}

期望和汉字的验证效果一致

[wenlng]

1. 设置英文字符集

chars := "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"

_ = capt.SetRangChars(strings.Split(chars, ""))

capt = captcha.GetCaptcha()

dots, b64, tb64, key, err := capt.Generate()

2. 前端点选结果

{"dot":"110,198,48,88,197,72","key":"c39190357e6e59043729c59a8fa99a71"}

3. 实际点选结果
   {"0":{"Index":0,"Dx":105,"Dy":227,"Size":38,"Width":38,"Height":38,"Text":"N","Angle":330,"Color":"#fcb08e","Color2":"#6e3700"},"1":{"Index":1,"Dx":50,"Dy":111,"Size":31,"Width":31,"Height":31,"Text":"A","Angle":20,"Color":"#60c1ff","Color2":"#6e3700"},"2":{"Index":2,"Dx":193,"Dy":96,"Size":37,"Width":37,"Height":37,"Text":"F","Angle":325,"Color":"#b4fed4","Color2":"#660033"}}

期望和汉字的验证效果一致

嘿嘿，v2 的位置计算将更精准了，即将发布，可关注一下！