Remove nullptr dereference.

Bug: 62799790
Test: vts_ibase_test
Change-Id: Ia80d83ef03bc8737b3f1c43ce688987309376fa1
diff --git a/host/hal_generic/generic_context_hub.cc b/host/hal_generic/generic_context_hub.cc
index b8962da..5cc2bd9 100644
--- a/host/hal_generic/generic_context_hub.cc
+++ b/host/hal_generic/generic_context_hub.cc
@@ -64,7 +64,7 @@
  */
 int hidlHandleToFileDescriptor(const hidl_handle& hh) {
   const native_handle_t *handle = hh.getNativeHandle();
-  return (handle->numFds >= 1) ? handle->data[0] : -1;
+  return (handle != nullptr && handle->numFds >= 1) ? handle->data[0] : -1;
 }
 
 }  // anonymous namespace