bindings: Add empty checks for toV8()

Source/bindings/templates/methods.cpp

 {% from 'conversions.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value %}
 
 
 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
 {% if method.returns_promise and method.has_exception_state %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}Promise(const v8::FunctionCallbackInfo<v8::Value>& info, ExceptionState& exceptionState)
 {% else %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
@@ skipping 512 matching lines @@
     v8::Local<v8::Context> contextInPrivateScript = toV8Context(frame, DOMWrapperWorld::privateScriptIsolatedWorld());
     if (contextInPrivateScript.IsEmpty())
         return false;
     ScriptState* scriptState = ScriptState::from(contextInPrivateScript);
     ScriptState* scriptStateInUserScript = ScriptState::forMainWorld(frame);
     if (!scriptState->executionContext())
         return false;
 
     ScriptState::Scope scope(scriptState);
     v8::Local<v8::Value> holder = toV8(holderImpl, scriptState->context()->Global(), scriptState->isolate());
+    if (holder.IsEmpty())
+        return false;
 
     {% for argument in method.arguments %}
     v8::Local<v8::Value> {{argument.handle}} = {{argument.private_script_cpp_value_to_v8_value}};
     {% endfor %}
     {% if method.arguments %}
     v8::Local<v8::Value> argv[] = { {{method.arguments | join(', ', 'handle')}} };
     {% else %}
     {# Empty array initializers are illegal, and don\t compile in MSVC. #}
     v8::Local<v8::Value> *argv = 0;
     {% endif %}
@@ skipping 98 matching lines @@
                   method.exposed_test) %}
 {% filter runtime_enabled(method.overloads.runtime_enabled_function_all
                           if method.overloads else
                           method.runtime_enabled_function) %}
 prototypeObject->Set(v8AtomicString(isolate, "{{method.name}}"), v8::FunctionTemplate::New(isolate, {{cpp_class_or_partial}}V8Internal::{{method.name}}MethodCallback, v8Undefined(), defaultSignature, {{method.number_of_required_arguments}})->GetFunction(isolate->GetCurrentContext()).ToLocalChecked());
 {% endfilter %}{# runtime_enabled() #}
 {% endfilter %}{# exposed() #}
 {% endfor %}
 {% endif %}
 {%- endmacro %}