修bug，没有选中节点按enter和tab键报错

src/module/editor.js

@@ -142,6 +142,9 @@ KityMinder.registerModule( "TextEditModule", function () {
                 if(cmds[e.commandName]){
 
                     var node = km.getSelectedNode();
+                    if( !node ){
+                        return;
+                    }
 
                     var textShape = node.getTextShape();
 

src/module/layout.js

@@ -106,6 +106,11 @@ KityMinder.registerModule( "LayoutModule", function () {
 			base: Command,
 			execute: function ( km, node, focus, silbling ) {
 				var parent = km.getSelectedNode();
+
+				if( !parent ){
+					return null;
+				}
+
 				if ( parent.getType() !== "root" && parent.getChildren().length !== 0 && parent.getData( "expand" ) === false ) {
 					km.expandNode( parent );
 				}
@@ -129,6 +134,9 @@ KityMinder.registerModule( "LayoutModule", function () {
 			base: Command,
 			execute: function ( km, node, focus ) {
 				var selectedNode = km.getSelectedNode();
+				if( !selectedNode ){
+					return null;
+				}
 
 				if ( selectedNode.isRoot() ) {
 					node.setType( "main" );