Fixed empty DocIdSetIterator

Change-Id: I322b10563b92898ce662788277761c356eac9221
diff --git a/.gitignore b/.gitignore
index 149acc4..80db8ed 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,3 +32,4 @@
 /src/test/java/de/ids_mannheim/korap/collection/TestWithExternalIndex.java
 /krill_cache/
 /vc
+/vc-cache
\ No newline at end of file