SamlWebFilter: Fix AnonymousHttpRequest.getHeaderNames method

Fix loop over header names.

Change-Id: I9f9648b6879579cc764a3ea14ceeadf6a70f8fa9
diff --git a/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java b/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java
index 5f0508e..f71398a 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/saml/SamlWebFilter.java
@@ -313,7 +313,7 @@
       while (wrappedHeaderNames.hasMoreElements()) {
         String header = wrappedHeaderNames.nextElement();
         if (!authHeaders.contains(header.toUpperCase())) {
-          headerNames.add(wrappedHeaderNames.nextElement());
+          headerNames.add(header);
         }
       }
       return Iterators.asEnumeration(headerNames.iterator());