TabAPI throws Error when Closing

[tsmaeder]

Bug Description:

I get exceptions in the browser log when closing editor tabs:

rpc-message-encoder.ts:184 Uncaught (in promise) Error: Tab close updated received for index 4 which does not exist
    at TabGroupExt.acceptTabOperation (C:\Users\thomas\code\EclipseSource\theia\packages\plugin-ext\lib\plugin\tabs.js:156:23)
    at TabsExtImpl.$acceptTabOperation (C:\Users\thomas\code\EclipseSource\theia\packages\plugin-ext\lib\plugin\tabs.js:286:27)
    at C:\Users\thomas\code\EclipseSource\theia\packages\plugin-ext\lib\common\proxy-handler.js:91:71
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async RpcProtocol.handleRequest (C:\Users\thomas\code\EclipseSource\theia\packages\core\lib\common\message-rpc\rpc-protocol.js:167:28)

Steps to Reproduce:

1. Open 4 editors
2. Close the second-to-last (third) tab
3. Close the last tab
4. Observe: you get the above exception

From a cursory inspection of the code, it seems that the TabInfo.tabIndex field is not updated upon deletion. So when I delete for the second time, it notifies the deletion with index 3, which doesn't exist.

Additional Information

• Operating System: Windows Electron
• Theia Version: master

[tsmaeder]

Tagging @jonah-iden, because he might know what's up.

[jonah-iden]

oh yeah, that seems like an inconsistency arises between the model in tabs-main and the actual tabs from phosphor. I can probably take a look at it tomorrow. Should be easy to fix