"each" helper throws "TypeError: ret.join is not a function" when the context is an empty list

[toverux]

This error appears to happen when empty sources are passed to the each helper that is overriden by this library.

It's this line that crashes :

handlebars-async-helpers/helpers/each.js

Line 108 in cc6ad44

return ret.join('')

The problem is that when the items count is 0, options.inverse() is called on the context and replaces the return value.
But by default, when each has no else condition, it's a noop that does not return an array but an empty string, making ret.join() crash.

Handlebars does not have this problem because they don't have to join : https://github.com/handlebars-lang/handlebars.js/blob/785a63e0a84bc5d6617fd1619baa975f1380ddbd/lib/handlebars/helpers/each.js#L80

This solution works, for example:

[ericalli]

I submitted PR #15 with the aforementioned fix and tests.