Ignore nullptr in native_handle_close().

Just like native_handle_delete().

Bug: http://b/143898343
Test: new test
Change-Id: I373067aa6c2b03548b218c7011bdbf23bd71f260
diff --git a/libcutils/native_handle.cpp b/libcutils/native_handle.cpp
index b409e5b..5804ab1 100644
--- a/libcutils/native_handle.cpp
+++ b/libcutils/native_handle.cpp
@@ -81,6 +81,8 @@
 }
 
 int native_handle_close(const native_handle_t* h) {
+    if (!h) return 0;
+
     if (h->version != sizeof(native_handle_t)) return -EINVAL;
 
     int saved_errno = errno;