fix: Fix disable stream when no manifest (#7497)

Author: avelad

lib/player.js

@@ -7258,6 +7258,10 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       return false;
     }
 
+    if (!this.manifest_) {
+      return false;
+    }
+
     // It only makes sense to disable a stream if we have an alternative else we
     // end up disabling all variants.
     const hasAltStream = this.manifest_.variants.some((variant) => {