fix: Abort operations only once (#7624)

Backported to v4.9.x

lib/util/abortable_operation.js

@@ -39,8 +39,8 @@ shaka.util.AbortableOperation = class {
     /** @private {function():!Promise} */
     this.onAbort_ = onAbort;
 
-    /** @private {boolean} */
-    this.aborted_ = false;
+    /** @private {?Promise} */
+    this.abortPromise_ = null;
   }
 
   /**
@@ -110,8 +110,10 @@ shaka.util.AbortableOperation = class {
    * @export
    */
   abort() {
-    this.aborted_ = true;
-    return this.onAbort_();
+    if (!this.abortPromise_) {
+      this.abortPromise_ = this.onAbort_();
+    }
+    return this.abortPromise_;
   }
 
   /**
@@ -166,7 +168,7 @@ shaka.util.AbortableOperation = class {
 
     const makeCallback = (isSuccess) => {
       return (value) => {
-        if (this.aborted_ && isSuccess) {
+        if (this.abortPromise_ && isSuccess) {
           // If "this" is not abortable(), or if abort() is called after "this"
           // is complete but before the next stage in the chain begins, we
           // should stop right away.