Release PduPersister if need to create a new one

Change-Id: I6bc0f49db70a205c03ee35d39694ca0c99a86451
Signed-off-by: Roger Chen <cxr514033970@gmail.com>
diff --git a/src/java/com/google/android/mms/pdu/PduPersister.java b/src/java/com/google/android/mms/pdu/PduPersister.java
index 94f1430..e9b9e26 100644
--- a/src/java/com/google/android/mms/pdu/PduPersister.java
+++ b/src/java/com/google/android/mms/pdu/PduPersister.java
@@ -292,7 +292,10 @@
 
     /** Get(or create if not exist) an instance of PduPersister */
     public static PduPersister getPduPersister(Context context) {
-        if ((sPersister == null) || !context.equals(sPersister.mContext)) {
+        if ((sPersister == null)) {
+            sPersister = new PduPersister(context);
+        } else if (!context.equals(sPersister.mContext)) {
+            sPersister.release();
             sPersister = new PduPersister(context);
         }