GitilesFilter: Ensure this.config is assigned

this.config was never set, thus a null reference was passed on.

Change-Id: I8ed25cadcefe886f330a10f03453f1e773c86ac5

gitiles-servlet/src/main/java/com/google/gitiles/GitilesFilter.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/GitilesFilter.java b/gitiles-servlet/src/main/java/com/google/gitiles/GitilesFilter.java
index 55826b9..c6a0396 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/GitilesFilter.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/GitilesFilter.java
@@ -296,7 +296,7 @@
       config = this.config;
     } else {
       try {
-        config = GitilesConfig.loadDefault(filterConfig);
+        this.config = config = GitilesConfig.loadDefault(filterConfig);
       } catch (IOException e) {
         throw new ServletException(e);
       } catch (ConfigInvalidException e) {