Fixed relilability issues in running health checks

Summary: Run doctor checks remained pending when the socket disonnected during a check. This

Reviewed By: aigoncharov

Differential Revision: D32984539

fbshipit-source-id: 277005e78803afaaa220cc5ca7fdc9cca6254453

desktop/flipper-ui-core/src/dispatcher/flipperServer.tsx

@@ -59,7 +59,7 @@ export function connectFlipperServerToStore(
             {'' + err}
           </>
         ) : (
-          <>Failed to start Flipper server: ${err.message}</>
+          <>Failed to start Flipper server: {err.message ?? err}</>
         ),
       duration: null,
     });