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/TunerDemux.cpp b/services/tuner/TunerDemux.cpp
index 8346992..ba8d6a7 100644
--- a/services/tuner/TunerDemux.cpp
+++ b/services/tuner/TunerDemux.cpp
@@ -222,6 +222,8 @@
     }
 
     Result res = mDemux->close();
+    mDemux = NULL;
+
     if (res != Result::SUCCESS) {
         return Status::fromServiceSpecificError(static_cast<int32_t>(res));
     }