fix: dedent error when EOF comes in a block of two or greater depth

[GreasySlug]

Fixes #315.

Dedent is automatically called if EOF is at the end of the block In this case, it is interpreted that no spaces are inserted, resulting in a problem where indentation and spaces do not match This caused an invalid indent error

Changes proposed in this PR:

• A ssigned whitespces length to var
• Add zero whitespace case

@mtshiba