preg_split returning false will cause TypeError on invalid countable in PHP 8

Michelf/MarkdownExtra.php

@@ -683,7 +683,7 @@ class MarkdownExtra extends \Michelf\Markdown {
 			// by the pattern.
 			$parts = preg_split($tag_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
 
-			if (count($parts) < 3) {
+			if ($parts === false || count($parts) < 3) {
 				// End of $text reached with unbalenced tag(s).
 				// In that case, we return original text unchanged and pass the
 				// first character as filtered to prevent an infinite loop in the