Fix code scanning alert no. 1: Prototype-polluting function

[alex-w]

Fixes https://github.com/Stellarium/stellarium/security/code-scanning/1

To fix the prototype pollution vulnerability in the extend function, we need to add checks to prevent the merging of special properties like __proto__ and constructor. This can be done by adding a condition to skip these properties during the merge process.

• General Fix: Add a condition to skip properties named __proto__ and constructor during the merge process.
• Detailed Fix: Modify the extend function to include a check that skips the properties __proto__ and constructor when copying properties from the source object to the target object.
• Specific Changes: Update the extend function in the file plugins/RemoteControl/webroot/js/globalize.js to include the necessary checks.
• Requirements: No additional methods or imports are needed. The changes will be made directly within the extend function.

Suggested fixes powered by Copilot Autofix. Review carefully before merging.