Fix: Should be able to insert tabs using tab key when not in a list

[codebykat]

Fix

In adding tabbing for lists in #2515 I accidentally disabled Tab key to insert tabs when not in a list. This PR restores the default behavior.

Test

1. Use Tab key within normal text; does it insert spaces at the cursor?
2. Use Tab key on empty line; does it insert spaces at the cursor?
3. Use Tab key inside a list item; does it change the nesting level of the entire line?

Release

N/A (update to #2515)