Wrong context when iterating an array with undefined inside a conditional block helper

[aleen42]

Recently I found that I have missed my context with the following snippet:

const Handlebars = require('handlebars');

Handlebars.compile('{{#each arr}}'
                   + '{{#if 1}}{{@index}}: {{../foo}}|{{/if}}'
                   + '{{/each}}')({
    arr : [1, 2, void 0, 4],
    foo : 'foo',
}); // => "0: foo|1: foo|2: |3: foo|"

Handlebars.compile('{{#each arr}}'
                   + '{{#if 0}}{{^}}{{@index}}: {{../foo}}|{{/if}}'
                   + '{{/each}}')({
    arr : [1, 2, void 0, 4],
    foo : 'foo',
}); // => "0: foo|1: foo|2: |3: foo|"

The problem only occurs inside a conditional block helper:

Handlebars.compile('{{#each arr}}'
                   + '{{@index}}: {{../foo}}|'
                   + '{{/each}}')({
    arr : [1, 2, void 0, 4],
    foo : 'foo',
}); // => "0: foo|1: foo|2: foo|3: foo|"

It is a common case that a conditional block helper should not create a new context, but actually, it has wrapped an empty context when iterating an array with undefined inside it.