send task manual doesn't succeed if label is not set

[clarsen]

When "Todoist: Send Task (manual)" is invoked and label is not specified, the UI shows "Task sent to Todoist" but doesn't show "Task sent successfully", and the task doesn't appear in todoist.

There's a silent failure logged in developer console:

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading '0')
when sendObj is being created and it isn't caught and shown in UI. That is due to label having value undefined.

See fix in #89