fixed website crash error by highscores

[Yash-Punia]

Error: The official A-Blast website crashes on opening because of some null value error in highscores.js file as of now.

Cause: The document.getElementById('save-score') was returning the null value which in turn crashed the code

Solution: I added a window.onload function to solve the error such that the dom request is made only after the window is loaded