Fix double free in MPEG4Extractor

Bug: 113341381
Test: yes
Change-Id: I6ae1cb03b04fa1d9b664a0ca8b29a21f60bd6bc3
diff --git a/media/extractors/mp4/MPEG4Extractor.cpp b/media/extractors/mp4/MPEG4Extractor.cpp
index c02d2fb..f52d451 100644
--- a/media/extractors/mp4/MPEG4Extractor.cpp
+++ b/media/extractors/mp4/MPEG4Extractor.cpp
@@ -393,7 +393,9 @@
     }
     mPssh.clear();
 
-    delete mCachedSource;
+    if (mCachedSource != mDataSource) {
+        delete mCachedSource;
+    }
     delete mDataSource;
 }