Fix whitespace with XHTML parser

Remove leading whitespace in codeblocks that only appears when using
browser XHTML parsers for some reason.

scripts/xhtmlize-single-file.sh

@@ -52,5 +52,5 @@ sed 7d "$html_file" | run_xmllint | tail -n +2 >"$tmp_file"
 		-e 's#</span>(<a[^>]*rel="(nofollow ugc|ugc nofollow)"([^>]*)?>liked</a>)#</span> \1#' \
 		-e 's#^[\t\s]*<(code|/pre)#<\1#' \
 		"$tmp_file" \
-		| awk '/^<\/code>/{printf "%s",$0;next}7'
+		| awk '/(^<\/code>|<pre tabindex="0">)/{printf "%s",$0;next}7'
 } >"$html_file"