Fix OOB error in WP_Token_Map when reaching the end of a group with n…

…o matches.

src/wp-includes/class-wp-token-map.php

@@ -545,7 +545,7 @@ public function read_token( $text, $offset = 0, &$matched_token_byte_length = nu
 			$group        = $this->large_words[ $group_at / ( $this->key_length + 1 ) ];
 			$group_length = strlen( $group );
 			$at           = 0;
-			while ( $at < $group_length ) {
+			while ( $at + $this->key_length < $group_length ) {
 				$token_length   = unpack( 'C', $group[ $at++ ] )[1];
 				$token          = substr( $group, $at, $token_length );
 				$at            += $token_length;