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.
Built from https://develop.svn.wordpress.org/trunk@44325


git-svn-id: http://core.svn.wordpress.org/trunk@44155 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44324';
+$wp_version = '5.1-alpha-44325';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.