fix(Ads): Fix usage of ENABLE-SKIP-AFTER and ENABLE-SKIP-FOR (#7677)

Author: avelad

lib/ads/interstitial_ad_manager.js

@@ -954,14 +954,14 @@ shaka.ads.InterstitialAdManager = class {
         const skipControl = dataAsJson['SKIP-CONTROL'];
         if (skipControl) {
           const enableSkipAfterValue = skipControl['ENABLE-SKIP-AFTER'];
-          if (enableSkipAfterValue instanceof Number) {
+          if ((typeof enableSkipAfterValue) == 'number') {
             skipOffset = parseFloat(enableSkipAfterValue);
             if (isNaN(enableSkipAfterValue)) {
               skipOffset = isSkippable ? 0 : null;
             }
           }
           const enableSkipForValue = skipControl['ENABLE-SKIP-FOR'];
-          if (enableSkipForValue instanceof Number) {
+          if ((typeof enableSkipForValue) == 'number') {
             skipFor = parseFloat(enableSkipForValue);
             if (isNaN(enableSkipForValue)) {
               skipFor = null;