go.talks/pkg/present: fix named highlights

Previously it wasn't stripping "// HLfoo" comments from lines.

R=campoy, campoy
CC=golang-dev
https://golang.org/cl/7193054
diff --git a/pkg/present/code.go b/pkg/present/code.go
index 43b3867..e27c42b 100644
--- a/pkg/present/code.go
+++ b/pkg/present/code.go
@@ -261,6 +261,10 @@
 			continue
 		}
 		line := m[1]
+		if m[2] != "" && m[2] != label {
+			lines[i] = line
+			continue
+		}
 		space := ""
 		if j := strings.IndexFunc(line, func(r rune) bool {
 			return !unicode.IsSpace(r)
@@ -268,9 +272,7 @@
 			space = line[:j]
 			line = line[j:]
 		}
-		if m[2] == "" || m[2] == label {
-			lines[i] = space + "<b>" + line + "</b>"
-		}
+		lines[i] = space + "<b>" + line + "</b>"
 	}
 	return strings.Join(lines, "\n")
 }