Saving term broken. If no term parent is set - sets to term ID 1.

[mattheu]

This was introduced by the fix for ticket #17646

When saving a term with no parent selected - the parent is saved as term 1. It should be set to 0. For non-category terms - this causes them to dissapear from the admin.

From category-template.php line 346 - The term parent select field uses -1 for none - and this is now cast to 1 by the sanitize_term_field function - which saves the term parent as 1.

I've added a patch that sets any negative values to 0.

[mattheu]

Updated patch to not use a ternary operator

[SergeyBiryukov]

25852-2.diff​ would not work as expected, since $value is already changed to 1 in line 1714. The check should also be inside the in_array() condition, not after it.

25852.3.diff​ reverts that part of [26010] and adds a basic unit test.

[SergeyBiryukov]

In 26028:

A negative term parent value should be sanitized to 0, not 1. Fix a regression in sanitize_term_field() caused by [26010].

props mattheu for initial patch.
fixes #25852.