Fix PHP 8.1 compatibility in ParserState::strsplit()

> Error Message: preg_split(): Passing null to parameter MyIntervals#3 ($limit) of type int is deprecated

see MyIntervals#338

(cherry picked from commit 84b3ba7)

lib/Sabberworm/CSS/Parsing/ParserState.php

@@ -282,7 +282,7 @@ private function strtolower($sString) {
 	private function strsplit($sString) {
 		if ($this->oParserSettings->bMultibyteSupport) {
 			if ($this->streql($this->sCharset, 'utf-8')) {
-				return preg_split('//u', $sString, null, PREG_SPLIT_NO_EMPTY);
+				return preg_split('//u', $sString, -1, PREG_SPLIT_NO_EMPTY);
 			} else {
 				$iLength = mb_strlen($sString, $this->sCharset);
 				$aResult = array();
@@ -307,4 +307,4 @@ private function strpos($sString, $sNeedle, $iOffset) {
 			return strpos($sString, $sNeedle, $iOffset);
 		}
 	}
-}
+}