css: highlight even table rows and skip empty rows

This is stolen from kernel.org css [0].

[0] https://git.kernel.org/cgit-korg-0.10.1.css
diff --git a/ui-log.c b/ui-log.c
index 6cc81a3..3220fd9 100644
--- a/ui-log.c
+++ b/ui-log.c
@@ -263,8 +263,9 @@
 
 	html("</td></tr>\n");
 
-	if (revs->graph || ctx.qry.showmsg) { /* Print a second table row */
-		html("<tr class='nohover'>");
+	if ((revs->graph && !graph_is_commit_finished(revs->graph))
+			|| ctx.qry.showmsg) { /* Print a second table row */
+		html("<tr class='nohover-highlight'>");
 
 		if (ctx.qry.showmsg) {
 			/* Concatenate commit message + notes in msgbuf */