add assert

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1135509 13f79535-47bb-0310-9956-ffa450edef68

lucene/src/java/org/apache/lucene/index/CompoundFileReader.java

@@ -55,6 +55,7 @@ public class CompoundFileReader extends Directory {
   }
   
   public CompoundFileReader(Directory dir, String name, int readBufferSize) throws IOException {
+    assert !(dir instanceof CompoundFileReader) : "compound file inside of compound file: " + name;
     directory = dir;
     fileName = name;
     this.readBufferSize = readBufferSize;