fix: memory leak in codelens controller

[SimonSiefke]

Before:

In the code lens controller, the old code lens models don't seem to be cleared in all cases. It seems they are only cleared if toResolve.length is greater than zero. Due to the early return, the cleanup seems missing for the case toResolve.length === 0 .

// before
private _resolveCodeLensesInViewport(): void {

    /* ... */
    if (toResolve.length === 0) {
	    return; 
    }

    /* ... */ 
    this._oldCodeLensModels.clear();
}

---

After:

The change is to clear oldCodeLensModels in both cases:

// after
private _resolveCodeLensesInViewport(): void {

    /* ... */
    if (toResolve.length === 0) {
		this._oldCodeLensModels.clear();
	    return; 
    }

    /* ... */ 
    this._oldCodeLensModels.clear();
}

[mjbvz]

Thanks!