support removing all data from tasks.json

[elaihau]

• When all data are removed from tasks.json, or data in tasks.json is
  corrupted, Theia fails to update tasks that have been loaded into the
  memory. This pull request fixes this bug.
• fixes emtpy tasks.json are not handled properly #6032

Signed-off-by: Liang Huang liang.huang@ericsson.com

How to test

• Open a workspace that has: at least one detected task, and a tasks.json where at least one detected task is customized
• Open the "Run task"
  • Expected: The customized detected tasks should be displayed as "Configured tasks".
• Remove all data from tasks.json. Save changes.
• Open the "Run task" again
  • Expected: all detected tasks should be displayed as "detected tasks", as the customizations have been removed from tasks.json

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

[vince-fugnitto]

It works for me :)

I tested the following:

1. open a workspace with the vscode npm built-in extension present
2. configure a task (ex: npm prepare)
3. execute run task (npm prepare is displayed as a configured task)
4. remove the content from the tasks.json
5. execute run task again (npm prepare is reset and now displayed as a detected task)

When testing on master, step 5 would still display the task as configured.
The bug is therefore fixed 👍

[elaihau]

Thank you Vincent !