Fix bad exit status 255 generated by uncaught TypeError

The error_get_last function returns NULL if there hasn't been an error
yet, Says from from https://secure.php.net/error_get_last.

    PHP Fatal error:  Uncaught TypeError: Return value of TheSeer\phpDox\ErrorHandler::getLastError() must be of the type array,
    null returned in /net/enterprise-data1/home/ad min/gasolwu/Code/phpdox/src/shared/ErrorHandler.php:147
    Stack trace:
    #0 /net/enterprise-data1/home/admin/gasolwu/Code/phpdox/src/shared/ErrorHandler.php(55): TheSeer\phpDox\ErrorHandler->getLastError()
    #1 [internal function]: TheSeer\phpDox\ErrorHandler->handleShutdown()
    #2 {main}
      thrown in /net/enterprise-data1/home/admin/gasolwu/Code/phpdox/src/shared/ErrorHandler.php on line 147

Author: Gasol Wu

src/shared/ErrorHandler.php

@@ -140,7 +140,9 @@ private function renderException($exception): void {
     private function getLastError(): array {
         $error = \error_get_last();
 
-        if ($error && $error['type'] === \E_USER_NOTICE) {
+        if ($error == null) {
+            return [];
+        } elseif ($error['type'] === \E_USER_NOTICE) {
             return [];
         }