Exporter gets stuck in a loop a loop/break in the category hierarchy

[westi]

Ideally it should be impossible for a loop/incorrect parentage in a category hierarchy to exist.

But sometimes they do.

If one does exist then export_wp() gets stuck :(

It gets stuck in this code:

		// put categories in order with no child going before its parent
		while ( $cat = array_shift( $categories ) ) {
			if ( $cat->parent == 0 || isset( $cats[$cat->parent] ) )
				$cats[$cat->term_id] = $cat;
			else
				$categories[] = $cat;
		}

Similar to #20635 but different.

Simple fix using term_exits to check that the parent of a term exists before adding to the array to try again later.

Patch looks sensible.

This uses to have a looping guard prior to [15961] so setting Version to 3.1

Improved patch - term_exists only tests true ints as term_ids :(

Found a "fun" bug in my patch - I assumed that term_exists would use something like is_numeric to decide if I was giving it an ID instead of a slug but it uses is_int() and this code was failing to work correctly.