Currently, when 'shiftwidth' is set to 0, GetLedgerIndent always returns
0, making it very ineffective.
But when 'shiftwidth' is set to 0, vim falls back to 'tabstop'. The help
entry of 'shiftwidth' recommends to use the shiftwidth function to get
the effective value of 'shiftwidth', which is what this fix does.
Currently, when 'shiftwidth' is set to 0, GetLedgerIndent always returns 0, making it very ineffective.
But when 'shiftwidth' is set to 0, vim falls back to 'tabstop'. The help entry of 'shiftwidth' recommends to use the shiftwidth function to get the effective value of 'shiftwidth', which is what this fix does.