fix: Don't allow MSE reset in middle of a reset (#8338)

Author: avelad

lib/media/media_source_engine.js

@@ -2241,6 +2241,9 @@ shaka.media.MediaSourceEngine = class {
    * @private
    */
   async reset_(streamsByType) {
+    if (this.reloadingMediaSource_) {
+      return;
+    }
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
     this.reloadingMediaSource_ = true;
     this.needSplitMuxedContent_ = false;