Fix subtle bug for SIMD finding new line in chapter 10-4

[YukunJ]

Brief:

• the code might be incorrect when there are more than 1 newliner \n in 8-byte chunks. Since we are shifting mask after we find a newliner, eolPos is a relative position (relative to mask) in this chunk. But uint32_t curLen = (pos - lineBeginPos) + eolPos; is an absolute position.

• understood this is just demo purpose. But shift 8 bytes is UB.

I had a test version on this working here (dendibakh/perf-ninja@cf70700)

[dendibakh]

Yes, I decided to keep the code as simple as possible.
Changing the listing also requires also changing surrounding text as there are references to the line numbers.
Instead of fixing the code, I would rather add a footnote or a sentence in the text that there is an UB.

[YukunJ]

Sure that makes sense. I will add a comment for that.