Prevent double-closing of native handle in HidlMemory

Since the handle wasn't nullified, when the memory is explicitly
closed, the finalizer would attempt to close again, which results in
an exception.

Bug: 189213084
Test: Manual verification of ST use-cases, which uses this.
      Patch sent to partner for verification.
Change-Id: I4ac6bbdd88b3f729a022896adfed00effec48bd8

core/java/android/os/HidlMemory.java

@@ -79,6 +79,7 @@ public class HidlMemory implements Closeable {
     public void close() throws IOException {
         if (mHandle != null) {
             mHandle.close();
+            mHandle = null;
         }
     }