Avoid duplicate closing on Tuner instances

set all the successfully closed instance to null
to avoid duplicate closing on the same instance.

Test: make
Bug: 176190508
Change-Id: Ie96a5de3dcc1c40a594b4bb94bf31e546a77eb40
diff --git a/media/jni/tuner/DescramblerClient.cpp b/media/jni/tuner/DescramblerClient.cpp
index c9bacda..07be5cf 100644
--- a/media/jni/tuner/DescramblerClient.cpp
+++ b/media/jni/tuner/DescramblerClient.cpp
@@ -101,14 +101,18 @@
 Result DescramblerClient::close() {
     if (mTunerDescrambler != NULL) {
         Status s = mTunerDescrambler->close();
+        mTunerDescrambler = NULL;
         return ClientHelper::getServiceSpecificErrorCode(s);
     }
 
     if (mDescrambler != NULL) {
-        return mDescrambler->close();
+        Result res = mDescrambler->close();
+        mDescrambler = NULL;
+        return res;
     }
 
-    return Result::INVALID_STATE;}
+    return Result::INVALID_STATE;
+}
 
 /////////////// DescramblerClient Helper Methods ///////////////////////