Improve performance of File\X509->_mapInExtensions() for large arrays
Improve performance of File\X509->_mapInExtensions() for large arrays

This avoids passing array references by-value to is_array()
(which would trigger a copy) by refactoring _subArray() into
a separate is_array() check on a by-value var, and a separate
unchecked reference return.

phpseclib/phpseclib,metaclassing/phpseclib,danog/phpseclib,metaclassing/phpseclib,danog/phpseclib,terrafrost/phpseclib