add logging to CORS optimization

[xenoterracide]

I just spent hours trying to figure out why my cors configuration wasn't working. It turns out that it was. The problem was how I was testing it. There's an optimization

spring-framework/spring-web/src/main/java/org/springframework/web/cors/CorsUtils.java

Line 43 in 4e6532f

if (origin == null) {

on whether to output the headers that requires you to set the origin header. That's fair, but could you add some kind of log statement along this path that they they are being skipped? I don't care if it's debug or trace logging (although I think I prefer debug since I only put trace on spring security). I feel like stepping through this with a debugger isn't something I should have to do.