WP_Query taxonomy query vars should be set to first of multiple taxonomies.

This provides better parity with `get_queried_object()`, which will return the
first taxonomy/term matched by the current query.

[29891] introduced the abnormal behavior for the 'taxonomy' and 'term'
query vars.

Props Chouby.
Fixes #35619.

git-svn-id: https://develop.svn.wordpress.org/trunk@36484 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/query.php

@@ -2857,6 +2857,9 @@ class WP_Query {
 						} else {
 							$q['term_id'] = $queried_items['terms'][0];
 						}
+
+						// Take the first one we find.
+						break;
 					}
 				}
 			}