Fix #64745 hash_pbkdf2 truncation issue

When using hash_pbkdf2 with hex output and 0 length (auto), it incorrectly
truncates the result to 1/2 the expected result.
Merge branch 'PHP-5.5'

* PHP-5.5:
  Fix #64745 hash_pbkdf2 truncation issue
Fixed crash during search in empty persistent HashTable
Merge branch 'PHP-5.5'

* PHP-5.5:
  Fixed crash during search in empty persistent HashTable
Merge branch 'master' of git.php.net:php-src

* 'master' of git.php.net:php-src:
  Fix #64745 hash_pbkdf2 truncation issue