Update FileMakerConnection.php

The $response variable is not checked before method getBody() is called 
It happens to me when working on a local environment without an internet connection to the server. The $response variable is null and it crashes without generating a specific exception.

This small fix allows the program to continue and finally returns a ConnectionException

Author: andrez89

src/Services/FileMakerConnection.php

@@ -687,7 +687,7 @@ protected function retryMiddleware()
                 $log_message = 'Connection Error: ' . $exception->getMessage();
             }
 
-            $contents = $response->getBody()->getContents();
+            $contents = $response?->getBody()->getContents();
             $contents = json_decode($contents, true);
             if ($response && $response->getStatusCode() !== 200 && $contents !== null) {
                 $code = (int) Arr::first(Arr::pluck(Arr::get($contents, 'messages'), 'code'));