自定义拖动事件，只有一个节点时，拖动无反应 #4414

Describe the bug

自己写的拖动事件，然后只有一个节点时，节点就不能拖；大于一个时，就拖动正常

Your Example Website or App

https://codesandbox.io/p/github/Tina75/graph-test/master?file=%2FREADME.md&workspace=%257B%2522activeFilepath%2522%253A%2522%252FREADME.md%2522%252C%2522openFiles%2522%253A%255B%2522%252FREADME.md%2522%255D%252C%2522sidebarPanel%2522%253A%2522EXPLORER%2522%252C%2522gitSidebarPanel%2522%253A%2522COMMIT%2522%252C%2522spaces%2522%253A%257B%2522clf90chvp000x3n6snid14i6r%2522%253A%257B%2522key%2522%253A%2522clf90chvp000x3n6snid14i6r%2522%252C%2522name%2522%253A%2522Default%2522%252C%2522devtools%2522%253A%255B%257B%2522key%2522%253A%2522clg4gaax3000x3n6ixle6sfg8%2522%252C%2522type%2522%253A%2522PROJECT_SETUP%2522%252C%2522isMinimized%2522%253Afalse%257D%252C%257B%2522type%2522%253A%2522PREVIEW%2522%252C%2522taskId%2522%253A%2522dev%2522%252C%2522port%2522%253A5173%252C%2522key%2522%253A%2522clg4g1hyx006c3n6ij1rscuva%2522%252C%2522isMinimized%2522%253Afalse%252C%2522path%2522%253A%2522%252F%2523%252Fg6demo%2522%257D%252C%257B%2522type%2522%253A%2522TASK_LOG%2522%252C%2522taskId%2522%253A%2522dev%2522%252C%2522key%2522%253A%2522clg4g1gfp00343n6i7876lyjb%2522%252C%2522isMinimized%2522%253Afalse%257D%255D%257D%257D%252C%2522currentSpace%2522%253A%2522clf90chvp000x3n6snid14i6r%2522%252C%2522spacesOrder%2522%253A%255B%2522clf90chvp000x3n6snid14i6r%2522%255D%252C%2522hideCodeEditor%2522%253Afalse%257D

Steps to Reproduce the Bug or Issue

1、选择g6Demo路由，拖动节点

Expected behavior

该节点能够跟着鼠标正常拖动

Screenshots or Videos

No response

Platform

• OS: Windows
• Browser: [e.g. Chrome, Safari, Firefox]
• Version: [e.g. 91.1]

Additional context

No response