Desktop: Enforce that whitespace check for unindent checks the begining of the string

[CalebJohn]

Current behaviour is that if a Shift+Tab is pressed on a list item that is not indented, then it will mangle the start of the line

example

- something
- something // Shift+Tab

--->

- something
- - mething

This I was checking for whitespace but not enforcing that the check had to be at the start of a string. meaning - matched as true when it should not have. This fix updates the regex to enforce whitespace at the start.

[laurent22]

Makes sense, thanks for the fix!

[laurent22]

Makes sense, thanks for the fix!