Fix API.native_react_component arity issue

Always return false when user supply nothing

Author: zetachang

lib/react/api.rb

@@ -34,7 +34,8 @@ def self.eval_native_react_component(name)
       component
     end
 
-    def self.native_react_component?(name)
+    def self.native_react_component?(name = nil)
+      return false unless name
       eval_native_react_component(name)
     rescue
       nil

spec/react/native_library_spec.rb

@@ -69,7 +69,7 @@ class NestedComponent < React::Component::Base
     expect(React::API.native_react_component?(`window.NativeComponent`)).to be_truthy
     expect(React::API.native_react_component?(`{render: function render() {}}`)).to be_falsy
     expect(React::API.native_react_component?(`window.DoesntExist`)).to be_falsy
-    expect(React::API.native_react_component?(``)).to be_falsy
+    expect(React::API.native_react_component?()).to be_falsy
   end
 
   it "will import a React.js library into the Ruby name space" do