chore: Ignore main thread and frame callback return values

We don't do anything with the return value from these callbacks, so it's
OK to ignore them and not convert them to a local handle.

Author: ptomato

test-app/runtime/src/main/cpp/CallbackHandlers.cpp

@@ -700,11 +700,10 @@ int CallbackHandlers::RunOnMainThreadFdCallback(int fd, int events, void *data)
     auto context = it->second.context_.Get(isolate);
     Context::Scope context_scope(context);
     Local<v8::Function> cb = it->second.callback_.Get(isolate);
-    Local<Value> result;
 
     v8::TryCatch tc(isolate);
 
-    if (!cb->Call(context, context->Global(), 0, nullptr).ToLocal(&result)) {}
+    cb->Call(context, context->Global(), 0, nullptr);  // ignore JS return value
 
     cache_.erase(it);
 

test-app/runtime/src/main/cpp/CallbackHandlers.h

@@ -362,15 +362,11 @@ namespace tns {
                     v8::Context::Scope context_scope(context);
 
                     v8::Local<v8::Function> cb = entry->callback_.Get(isolate);
-                    v8::Local<v8::Value> result;
-
                     v8::Local<v8::Value> args[1] = {v8::Number::New(isolate, ts)};
 
                     v8::TryCatch tc(isolate);
 
-                    if (!cb->Call(context, context->Global(), 1, args).ToLocal(&result)) {
-                        // TODO
-                    }
+                    cb->Call(context, context->Global(), 1, args);  // ignore JS return value
 
                     frameCallbackCache_.erase(entry->id);  // invalidates *entry