BlameServlet: Fix check for regular file

To test if the tree entry is a file we must use
the mask and compare against the bits.

Change-Id: Iccc8928e24c4015cef0866398e17f49f1a987b4f

gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
index daae821..2bb9dd3 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
@@ -197,7 +197,7 @@
       }
       RevTree tree = rw.parseTree(commitId);
       TreeWalk tw = TreeWalk.forPath(rw.getObjectReader(), view.getPathPart(), tree);
-      if (tw == null || (tw.getRawMode(0) & FileMode.TYPE_FILE) == 0) {
+      if (tw == null || (tw.getRawMode(0) & FileMode.TYPE_MASK) != FileMode.TYPE_FILE) {
         return null;
       }
       return tw.getObjectId(0);