Saves to "und" instead of default language.

This is a "fun" edge-case:
* You have a bundle with the "multilingual" flag turned on (but internationalzation is disabled).
* The default language is *not* LANGUAGE_NONE (und), but some other language.
* You save the entity in the default language (let's say "en").
* You re-edit the entity, and save again (in my case using IEF).
* ECK saves your new value under "und" instead of "en" as it should.

ECK is assuming LANGUAGE_NONE is the default language before using field_attach_form(), which is unnecessary and inaccurate in this case.

Simply changing LANGUAGE_NONE to NULL for field_attach_form() to discern the $langcode on it's own solves this.