To clear the status lines, they should be set to an empty array to
prevent future updates of those lines. Setting the status lines to an
array containing an empty string is wrong as this causes the output to
continuously add that empty status line after each message.
`writeStatus` also cleans no longer used status lines.
The old code actually cleaned one line too much. However, as that line
was never used it makes no difference.
x/text/width.LookupRune has to re-encode its argument as UTF-8,
while LookupString operates on the UTF-8 directly.
The uint casts get rid of a bounds check.
Benchmark results, with b.ResetTimer introduced first:
name old time/op new time/op delta
TruncateASCII-8 69.7ns ± 1% 55.2ns ± 1% -20.90% (p=0.000 n=20+18)
TruncateUnicode-8 350ns ± 1% 171ns ± 1% -51.05% (p=0.000 n=20+19)
