Fix edge case around nested empty partials

[cmrschwarz]

This solves an edge case regarding nested, empty partials.
We currently don't restore our trailing newline flag when exiting a partial / helper.
This assumption fails if the partial doesn't produce any content at all.
This PR solves this.

Example testcase:

{{~#*inline "empty_partial"}}{{/inline}}
{{~#*inline "indented_partial"}}
{{>empty_partial}}foo
{{/inline}}
    {{>indented_partial}}

Output Before

foo

Output After

    foo

[coveralls]

coverage: 81.472% (+0.08%) from 81.389%
when pulling c60ef28 on cmrschwarz:recursive_empty_partials_fix
into 913784b on sunng87:master.