avoid using _.each on set method

[wellingguzman]

Models with an attribute named 'length' will make this each work as an array.

From underscore docs

Note: Collection functions work on arrays, objects, and array-like objects such as arguments, NodeList and similar. But it works by duck-typing, so avoid passing objects with a numeric length property. It's also good to note that an each loop cannot be broken out of — to break, use _.find instead.

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I do not check for hasOwnProperty in the for statement in the new code because it's not done in Backbone either so, just to keep things the same.

Explanation:

We have been using trackit for a while with Directus. We used to have a weird bug that we weren't able to reproduce, after a long research and testing we find out the problem was _.each, we have models that represents columns, a column can have a length but when we use columns with small length number 10, 100, 255, this wasn't noticeable, then we started using MEDIUMTEXT and LONGTEXT which translate to a 16,777,215 and 4,294,967,295 which takes time to process an array of that length, blocking the page from a couple of seconds to minutes.