always record category even if unknown

Author: Vladimir Kotal

opengrok-web/src/main/java/org/opengrok/web/StatisticsFilter.java

@@ -79,10 +79,8 @@ public void doFilter(ServletRequest sr, ServletResponse sr1, FilterChain fc)
         String category;
         if (isRoot(httpReq)) {
             category = "root";
-        } else if (config.getPrefix() != Prefix.UNKNOWN) {
-            category = config.getPrefix().toString().substring(1);
         } else {
-            return;
+            category = config.getPrefix().toString().substring(1);
         }
 
         Timer categoryTimer = Timer.builder("requests.latency").