fix: Fix creation of new Stream object for each manifest request in D…

…ASH Live when using CEA (#5674)

Fixes #5672

lib/dash/dash_parser.js

@@ -522,7 +522,10 @@ shaka.dash.DashParser = class {
       // Just update the variants and text streams, which may change as periods
       // are added or removed.
       this.manifest_.variants = this.periodCombiner_.getVariants();
-      this.manifest_.textStreams = this.periodCombiner_.getTextStreams();
+      const textStreams = this.periodCombiner_.getTextStreams();
+      if (textStreams.length > 0) {
+        this.manifest_.textStreams = textStreams;
+      }
       this.manifest_.imageStreams = this.periodCombiner_.getImageStreams();
 
       // Re-filter the manifest.  This will check any configured restrictions on