Fix bufferhubd crash in buffer_hub-test

Add some null and valid check in constructors to prevent bufferhubd from
crash when user enter invalid params.

Test: "atest frameworks/native/libs/vr/libbufferhub/buffer_hub-test.cpp#TestCreateBufferHubBufferFails"
and check "adb logcat | grep bufferhub"
No crashing reports.
atest buffer_hub-test: passed
Fix: 118624156

Change-Id: I56e83808f38ab146f1fc61d1b736dd0be640503d
diff --git a/services/vr/bufferhubd/buffer_node.cpp b/services/vr/bufferhubd/buffer_node.cpp
index f8ec59d..e74a21f 100644
--- a/services/vr/bufferhubd/buffer_node.cpp
+++ b/services/vr/bufferhubd/buffer_node.cpp
@@ -34,6 +34,10 @@
   }
 
   metadata_ = BufferHubMetadata::Create(user_metadata_size);
+  if (!metadata_.IsValid()) {
+    ALOGE("BufferNode::BufferNode: Failed to allocate metadata.");
+    return;
+  }
   InitializeMetadata();
 }