Fix: avoid triggering a notice when an accept header without an equal sign is parsed

Author: theboolean

src/Header/AbstractAccept.php

@@ -170,7 +170,12 @@ protected function getParametersFromFieldValuePart($fieldValuePart)
             foreach ($paramsStrings as $param) {
                 $explode = explode('=', $param, 2);
 
-                $value = trim($explode[1]);
+                if (count($explode) === 2) {
+                    $value = trim($explode[1]);
+                } else {
+                    $value = trim($param);
+                }
+
                 if (isset($value[0]) && $value[0] == '"' && substr($value, -1) == '"') {
                     $value = substr(substr($value, 1), 0, -1);
                 }