fix: Reset lastMediaSourceReset when seeking to unbuffered part (#8339)

Author: avelad

lib/media/streaming_engine.js

@@ -877,6 +877,7 @@ shaka.media.StreamingEngine = class {
       const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
 
       if (!newTimeIsBuffered(type)) {
+        this.lastMediaSourceReset_ = 0;
         if (mediaState.segmentPrefetch) {
           mediaState.segmentPrefetch.resetPosition();
         }