Fix use of count in PHP 7.2

Author: alcaeus

src/PHPHtmlParser/Selector.php

@@ -168,8 +168,7 @@ protected function parseSelectorString($selector)
     protected function seek(array $nodes, array $rule, array $options)
     {
         // XPath index
-        if (count($rule['tag']) > 0 &&
-            count($rule['key']) > 0 &&
+        if (!empty($rule['tag']) &&
             is_numeric($rule['key'])
         ) {
             $count = 0;