Prevent Undefined array key 1 warnings

[fiwswe]

These warnings occur due to the incorrect assumption that explode(…, $match, 2) will return at least an array of length 2:

E_WARNING: Undefined array key 1
/var/www/dokuwiki/lib/plugins/blog/syntax/archive.php(29)
#0 /var/www/dokuwiki/lib/plugins/blog/syntax/archive.php(29): dokuwiki\ErrorHandler::errorHandler()
#1 /var/www/dokuwiki/inc/parser/handler.php(298): syntax_plugin_blog_archive->handle()
#2 /var/www/dokuwiki/inc/Parsing/Lexer/Lexer.php(269): Doku_Handler->plugin()
#3 /var/www/dokuwiki/inc/Parsing/Lexer/Lexer.php(196): dokuwiki\Parsing\Lexer\Lexer->invokeHandler()
#4 /var/www/dokuwiki/inc/Parsing/Lexer/Lexer.php(146): dokuwiki\Parsing\Lexer\Lexer->dispatchTokens()
#5 /var/www/dokuwiki/inc/Parsing/Parser.php(113): dokuwiki\Parsing\Lexer\Lexer->parse()
#6 /var/www/dokuwiki/inc/parserutils.php(234): dokuwiki\Parsing\Parser->parse()
#7 /var/www/dokuwiki/inc/parserutils.php(198): p_get_instructions()
#8 /var/www/dokuwiki/inc/parserutils.php(520): p_cached_instructions()
#9 /var/www/dokuwiki/inc/parserutils.php(299): p_render_metadata()
#10 /var/www/dokuwiki/inc/common.php(262): p_get_metadata()
#11 /var/www/dokuwiki/doku.php(101): pageinfo()
#12 {main}

Fix this by suppressing the warnings.

Note: Another fix might be to use the DokuWiki sexplode() function instead of explode().

[Klap-in]

Please do not use suppression but fix the errors instead please. For that purpose sexplode() is added to DokuWiki indeed. (As it is added to last two recent versions, it might affect backwards compatibility, but at least 2 releases is ok)

[fiwswe]

Note: I'm not sure null is the correct default here. Please critically check.