android: only consider backend ready once LocalBackend.Start() has finished

This prevents spurious crashes from a nullpointer when we attempt to call
localapi while app.localAPIHandler is still null.

Updates #cleanup

Signed-off-by: Percy Wegmann <percy@tailscale.com>

libtailscale/backend.go

@@ -119,7 +119,7 @@ func (a *App) runBackend(ctx context.Context) error {
 	}
 	configs := make(chan configPair)
 	configErrs := make(chan error)
-	b, err := newBackend(a.dataDir, a.directFileRoot, a.appCtx, a.store, func(rcfg *router.Config, dcfg *dns.OSConfig) error {
+	b, err := a.newBackend(a.dataDir, a.directFileRoot, a.appCtx, a.store, func(rcfg *router.Config, dcfg *dns.OSConfig) error {
 		if rcfg == nil {
 			return nil
 		}
@@ -254,7 +254,7 @@ func (a *App) runBackend(ctx context.Context) error {
 	}
 }
 
-func newBackend(dataDir, directFileRoot string, appCtx AppContext, store *stateStore,
+func (a *App) newBackend(dataDir, directFileRoot string, appCtx AppContext, store *stateStore,
 	settings settingsFunc) (*backend, error) {
 
 	sys := new(tsd.System)
@@ -344,6 +344,7 @@ func newBackend(dataDir, directFileRoot string, appCtx AppContext, store *stateS
 			log.Printf("Failed to start LocalBackend, panicking: %s", err)
 			panic(err)
 		}
+		a.ready.Done()
 	}()
 	return b, nil
 }

libtailscale/tailscale.go

@@ -36,7 +36,7 @@ func newApp(dataDir, directFileRoot string, appCtx AppContext) Application {
 		dataDir:        dataDir,
 		appCtx:         appCtx,
 	}
-	a.ready.Add(1)
+	a.ready.Add(2)
 
 	a.store = newStateStore(a.appCtx)
 	netmon.RegisterInterfaceGetter(a.getInterfaces)