cmd/tsconnect: block after starting esbuild dev server

Thanks to @davidbuzz for raising the issue in #13973.

Fixes #8272
Fixes #13973

Change-Id: Ic413e14d34c82df3c70a97e591b90316b0b4946b
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tsconnect/common.go

@@ -150,6 +150,7 @@ func runEsbuildServe(buildOptions esbuild.BuildOptions) {
 		log.Fatalf("Cannot start esbuild server: %v", err)
 	}
 	log.Printf("Listening on http://%s:%d\n", result.Host, result.Port)
+	select {}
 }
 
 func runEsbuild(buildOptions esbuild.BuildOptions) esbuild.BuildResult {