Fixup onLog for null vm for non-stream (Root) context.

Signed-off-by: John Plevyak <jplevyak@gmail.com>

Author: jplevyak

include/proxy-wasm/context_interface.h

@@ -179,6 +179,9 @@ struct RootInterface : public RootGrpcInterface {
    */
   virtual bool onDone() = 0;
 
+  // Call when the for logging not associated with a stream lifecycle (e.g. logging only plugin).
+  virtual void onLog() = 0;
+
   /**
    * Call when no further stream calls will occur.  This will cause the corresponding Context in the
    * VM to be deleted.

src/null/null_plugin.cc

@@ -472,7 +472,7 @@ void NullPlugin::onLog(uint64_t context_id) {
     registry_->proxy_on_log_(context_id);
     return;
   }
-  getContext(context_id)->onLog();
+  getContextBase(context_id)->onLog();
 }
 
 uint64_t NullPlugin::onDone(uint64_t context_id) {