Indent filter does not ignore empty lines

[dhruvkb]

When using the indent filter on a block, empty lines are also indented. This is a divergence between Jinja and Nunjucks behaviour and should be addressed.

For example, the template below

{% set content %}
This is some text

and this is some more text.
{% endset %}
{% set content = content | indent(2, true) %}
{{ content }}

when rendered produces

..This is some text
..
..and this is some more text.

instead of

..This is some text

..and this is some more text.

Jinja issue: pallets/jinja#681
Jinja PR: pallets/jinja#685