Leading whitespaces after indentation are not parsed correctly

[styrix560]

When parsing the string:

"
    foo
"

two of the white-spaces should be flagged as trailing white-space and two should remain with the string. Currently, both are marked as being trailing white-space.

The same error occurs when parsing

  foo
    bar

Here all four white-spaces in front of bar are marked as trailing, while only two of them should be.