fallbacksrc: Retry fallback stream on errors too

It was retrying but then nonetheless handling the error as fatal.

utils/fallbackswitch/src/fallbacksrc/imp.rs

@@ -2732,6 +2732,7 @@ impl FallbackSrc {
                 drop(state_guard);
                 element.notify("status");
                 element.notify("statistics");
+                return true;
             }
         }