Fix the bug that EXIF attributes are always cached.

b2039501
diff --git a/media/java/android/media/ExifInterface.java b/media/java/android/media/ExifInterface.java
index 645f3f6..6d7c0ae 100644
--- a/media/java/android/media/ExifInterface.java
+++ b/media/java/android/media/ExifInterface.java
@@ -128,7 +128,10 @@
     }
 
     public void setFilename(String filename) {
-        mFilename = filename;
+        if (mFilename == null || !mFilename.equals(filename)) {
+            mFilename = filename;
+            mCachedAttributes = null;
+        }
     }
 
     /**