lnrpc/watchtowerrpc: prevent watchtowerrpc panic when tower not active

lnrpc/watchtowerrpc/config_active.go

@@ -7,6 +7,9 @@ package watchtowerrpc
 // fields with struct tags are meant to parsed as normal configuration options,
 // while if able to be populated, the latter fields MUST also be specified.
 type Config struct {
+	// Active indicates if the watchtower is enabled.
+	Active bool
+
 	// Tower is the active watchtower which serves as the primary source for
 	// information presented via RPC.
 	Tower WatchtowerBackend

lnrpc/watchtowerrpc/handler.go

@@ -124,7 +124,7 @@ func (c *Handler) GetInfo(ctx context.Context,
 // isActive returns nil if the tower backend is initialized, and the Handler can
 // proccess RPC requests.
 func (c *Handler) isActive() error {
-	if c.cfg.Tower != nil {
+	if c.cfg.Active {
 		return nil
 	}
 	return ErrTowerNotActive

subrpcserver_config.go

@@ -216,6 +216,9 @@ func (s *subRPCServerConfigs) PopulateDependencies(cc *chainControl,
 		case *watchtowerrpc.Config:
 			subCfgValue := extractReflectValue(subCfg)
 
+			subCfgValue.FieldByName("Active").Set(
+				reflect.ValueOf(tower != nil),
+			)
 			subCfgValue.FieldByName("Tower").Set(
 				reflect.ValueOf(tower),
 			)