Fix bug where nested scopes don't resolve parent context

[jupp0r]

This change fixes a bug where for the template

{{#each b}}{{#if ../../a}}{{#each this}}{{this}}{{/each}}{{/if}}{{/each}}

and the input

{"a": [{"b": true}], "b": [[1, 2, 3],[4, 5]]}

the output 123 would be produced. The correct output 12345
is produced after the fix. While this change definitely fixes the problem,
a cleaner solution would be to have RenderContext implement the Clone trait and cloning it in the call to render in the each helper.

[sunng87]

Hi @jupp0r , thank you very much for this patch. As you said, a clone() function on RenderContext will fix this. So I added a derive function to RenderContext to clone all fields except writer.

There is a minor mistake in your template, the correct one is:
{{#each b}}{{#if ../a}}{{#each this}}{{this}}{{/each}}{{/if}}{{/each}}

This issue should be fixed in 84fd531 .

Thank you again for this patch.