Fix bug in authentication code

[] changed RequestHandler to log a warning instead of returning an error to the user when authentication failed. Unfortunately, it didn't handle the resulting absent value of AuthResult. I don't yet know why the tests pass, and plan to add a test to check for this situation, but I wanted to start by fixing the problem as soon as possible, as it seems like this would result in exceptions any time a request was handled which didn't pass authentication.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=149136265

java/google/registry/request/RequestHandler.java

@@ -173,6 +173,7 @@ public class RequestHandler<C> {
     if (!authResult.isPresent()) {
       logger.warning("Request would not have been authorized");
       // TODO(b/28219927): Change this to call rsp.sendError(SC_FORBIDDEN) and return
+      authResult = Optional.of(AuthResult.NOT_AUTHENTICATED);
     }
 
     // Build a new request component using any modules we've constructed by this point.