Ensure that taxonomy name passed to get_term() filters is non-empty.

Since [34997], the `$taxonomy` parameter of `get_term()` has been
optional. This created cases where the `$taxonomy` parameter, used
to concatenate names for some filters and passed as a parameter to
others, would be empty. This changeset ensures that it's never
empty by falling back on the `taxonomy` of the located term.

Props dlh.
Fixes #45698.

git-svn-id: https://develop.svn.wordpress.org/trunk@44325 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/taxonomy.php

@@ -840,6 +840,9 @@ function get_term( $term, $taxonomy = '', $output = OBJECT, $filter = 'raw' ) {
 		return null;
 	}
 
+	// Ensure for filters that this is not empty.
+	$taxonomy = $_term->taxonomy;
+
 	/**
 	 * Filters a taxonomy term object.
 	 *