Call observer onError only once

Author: oskarhane

src/v1/internal/stream-observer.js

@@ -39,6 +39,7 @@ class StreamObserver {
     this._queuedRecords = [];
     this._tail = null;
     this._error = null;
+    this._hasFailed = false;
   }
 
   /**
@@ -87,6 +88,10 @@ class StreamObserver {
    * @param {Object} error - An error object
    */
   onError(error) {
+    if(this._hasFailed) {
+      return;
+    }
+    this._hasFailed = true;
     if( this._observer ) {
       if( this._observer.onError ) {
         this._observer.onError( error );