Fix a leak from AACEncoder.cpp

bug - 3470617

Change-Id: I328e92bc1b2aca72e5856703dae00f957f40bc27
diff --git a/media/libstagefright/codecs/aacenc/AACEncoder.cpp b/media/libstagefright/codecs/aacenc/AACEncoder.cpp
index a8b1292..e4ff128 100644
--- a/media/libstagefright/codecs/aacenc/AACEncoder.cpp
+++ b/media/libstagefright/codecs/aacenc/AACEncoder.cpp
@@ -189,6 +189,9 @@
     delete mApiHandle;
     mApiHandle = NULL;
 
+    delete mMemOperator;
+    mMemOperator = NULL;
+
     mStarted = false;
 
     return OK;