Fix StringIndexOutOfBoundsException on page load.

Triggered if there are no git repos present.

Bug: Issue 101
Change-Id: I58fc7aa58f16de4f71e115e3eb97a99d87c66467

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

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/DefaultAccess.java b/gitiles-servlet/src/main/java/com/google/gitiles/DefaultAccess.java
index 6fc3211..0e435c6 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/DefaultAccess.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/DefaultAccess.java
@@ -161,6 +161,9 @@
 
   private String getRelativePath(String path) {
     String base = basePath.getPath();
+    if (path.equals(base)) {
+      return "";
+    }
     if (path.startsWith(base)) {
       return path.substring(base.length() + 1);
     }