HTML 解析时属性值带空格报错

[shuzijun]

描述问题 Describe the problem

解析html异常，当img的src属性带有空格时提示异常

例如html

<img src=" https://camo.githubusercontent.com/497f6a6416dc9701a219f440ad8239c90a4aa1e56272679dbe6e37f1c15028f1/68747470733a2f2f62336c6f672e6f72672f696d616765732f6272616e642f6c7574652d3132382e706e67" style="height:250px; width:250px"/>

粘贴到javascript/lute.html的文本框中，不能正常展示图片，控制台异常

lute.min.js:4 Uncaught Error: runtime error: slice bounds out of range
    at $callDeferred (lute.min.js:4)
    at $panic (lute.min.js:4)
    at AR (runtime.go:380)
    at $subslice (lute.min.js:4)
    at Object.$packages.github.com/88250/lute/parse.BS.ptr.isOpenTag (html_block.go:277)
    at Object.$packages.github.com/88250/lute/parse.BS.ptr.parseHTML (html_block.go:168)
    at AK (html_block.go:37)
    at Object.$packages.github.com/88250/lute/parse.BS.ptr.incorporateLine (blocks.go:162)
    at Object.$packages.github.com/88250/lute/parse.BS.ptr.parseBlocks (blocks.go:39)
    at Object.BN [as Parse] (parse.go:32)
    at Object.$packages.github.com/88250/lute.N.ptr.Markdown (lute.go:80)
    at Object.$packages.github.com/88250/lute.N.ptr.MarkdownStr (lute.go:91)
    at Object.e.$externalizeWrapper.e.$externalizeWrapper (lute.min.js:4)
    at js.go:144
    at Object.e.$externalizeWrapper.e.$externalizeWrapper [as MarkdownStr] (lute.min.js:4)
    at onMarkdown (lute.html:36)
    at HTMLTextAreaElement.oninput (lute.html:44)

期待的结果 Expected result

在可以正常解析

截屏或录像 Screenshot or video

版本环境 Version environment

• 版本 Version：0.30
• 操作系统 Operating system： windows
• 浏览器（如果使用）Browser (if used)：chrome

其他信息 Other information