Fix the issue where resource silently fails to load

[baothientran]

Fixes #9093

When request.deferred.resolve(result) get called in the function RequestScheduler.getRequestReceivedFunction(), the callback can potentially create a new deferred object and assign it to the existing request. But after the resolve() above is executed, the request.deferred is assigned to undefined, which accidentally removes the newly created deferred object. So the second call of RequestScheduler.getRequestReceivedFunction() for the same request will lead to error of request.undefined.resolve(result).

For the fix, I save the old deferred object first, then modify the state of request, and call the resolve() at the end. The fix is similar to the cancel function just in case it can have the same potential problem

@lilleyse Can you please take a look at it? Please let me know if I should add anything

[cesium-concierge]

Thanks for the pull request @baothientran!

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[lilleyse]

Nice catch @baothientran!