Fix regession: index out of range panic in reference link (#172, #173)

[tomkwok]

The previous fix got reverted/removed by new commits.

[rtfb]

What's up with the broken test?

[tomkwok]

Fixed.

[rtfb]

Thanks! Could you also please add a test that reproduces the issue? That would greatly diminish the chances such a regression would reoccur.

[tomkwok]

Done. And this is the naughty string: []:<

[dmitshur]

I can confirm the test case causes a panic without the fix:

panic: runtime error: index out of range [recovered]
    panic: runtime error: index out of range

goroutine 52 [running]:
panic(0x17afe0, 0xc82000c070)
    /usr/local/go/src/runtime/panic.go:464 +0x3e6
testing.tRunner.func1(0xc8201a4090)
    /usr/local/go/src/testing/testing.go:467 +0x192
panic(0x17afe0, 0xc82000c070)
    /usr/local/go/src/runtime/panic.go:426 +0x4e9
github.com/russross/blackfriday.scanLinkRef(0xc820106400, 0xc820272f20, 0x4, 0x8, 0x3, 0x4, 0x4, 0x0, 0x0, 0x0)

And the fix resolves it, while all tests pass.

LGTM. Shall we merge this @rtfb?

[dmitshur]

Friendly ping @rtfb.

[rtfb]

Yes! Sorry for the delay. I wanted to drill down the history to see when the regression happened, but couldn't find time for it until last night... Turns out I broke it with bcd6dd8 :-/. Now when I have it figured out, I can merge it and investigate later.

Thanks @tomkwok and @shurcooL!