Complete TunerTimeFilter implementation

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

Test: make
Bug: 159067322
Bug: 176190508
Change-Id: Idf445641b47f4d8ab4230f30cf6ea3abd4226cbc
diff --git a/services/tuner/TunerDvr.cpp b/services/tuner/TunerDvr.cpp
index c7227b6..db4e07b 100644
--- a/services/tuner/TunerDvr.cpp
+++ b/services/tuner/TunerDvr.cpp
@@ -154,6 +154,8 @@
     }
 
     Result res = mDvr->close();
+    mDvr = NULL;
+
     if (res != Result::SUCCESS) {
         return ::ndk::ScopedAStatus::fromServiceSpecificError(static_cast<int32_t>(res));
     }