PHP 8.0 | Tokenizer/PHP: bug fix

PHP 8.0 elevate a number of notices/warnings to errors, which now exposes a bug in the `goto` tokenizer logic.

Error: `Trying to access array offset on value of type null`

Fixed by making sure that the token being accessed is an array before trying to access it.

src/Tokenizers/PHP.php

@@ -1441,7 +1441,8 @@ function return types. We want to keep the parenthesis map clean,
                 && $token[0] === T_STRING
                 && isset($tokens[($stackPtr + 1)]) === true
                 && $tokens[($stackPtr + 1)] === ':'
-                && $tokens[($stackPtr - 1)][0] !== T_PAAMAYIM_NEKUDOTAYIM
+                && (is_array($tokens[($stackPtr - 1)]) === false
+                || $tokens[($stackPtr - 1)][0] !== T_PAAMAYIM_NEKUDOTAYIM)
             ) {
                 $stopTokens = [
                     T_CASE               => true,