Undefined index in _pad_term_counts()

[valendesigns]

When using wp_list_categories() in conjunction with a comma separated string of child category ID's and the 'show_count=1' option, the _pad_term_counts() function in taxonomy.php will return an undefined index notice on line 2806.

The fix below:

while ( isset($terms_by_id[$child]->parent) && $parent = $terms_by_id[$child]->parent ) {

In [19077]:

Avoid undefined index notices. Props SergeyBiryukov, valendesigns. fixes #18455