Remove invalid `continue` calls from WP_Tax_Query::get_sql_for_clause().

This was leftover code from the previous implementation, which used a `foreach()`
loop. See [29901].

Props nofearinc.
See #29738, #29718.
Built from https://develop.svn.wordpress.org/trunk@29931


git-svn-id: http://core.svn.wordpress.org/trunk@29683 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/taxonomy.php

@@ -1041,7 +1041,7 @@ class WP_Tax_Query {
 		} elseif ( 'NOT IN' == $operator ) {
 
 			if ( empty( $terms ) ) {
-				continue;
+				return $sql;
 			}
 
 			$terms = implode( ',', $terms );
@@ -1055,7 +1055,7 @@ class WP_Tax_Query {
 		} elseif ( 'AND' == $operator ) {
 
 			if ( empty( $terms ) ) {
-				continue;
+				return $sql;
 			}
 
 			$num_terms = count( $terms );