PhotosApi: $photoset should be an array

[arfevrier]

Hello,
Here a fix when using the librairy to import photo through Flickr2Piwigo. I got the following error when importing photos from my account:

<br />
<b>Fatal error</b>:  Uncaught TypeError: in_array(): Argument #2 ($haystack) must be of type array, null given in /config/www/plugins/flickr2piwigo/vendor/samwilson/phpflickr/src/PhotosApi.php:477
Stack trace:
#0 /config/www/plugins/flickr2piwigo/vendor/samwilson/phpflickr/src/PhotosApi.php(477): in_array()
#1 /config/www/plugins/flickr2piwigo/include/ws_functions.inc.php(147): Samwilson\PhpFlickr\PhotosApi-&gt;getSets()
#2 /app/www/public/include/ws_core.inc.php(600): ws_flickr2piwigo_importPhoto()
#3 /app/www/public/include/ws_protocols/rest_handler.php(41): PwgServer-&gt;invoke()
#4 /app/www/public/include/ws_core.inc.php(281): PwgRestRequestHandler-&gt;handleRequest()
#5 /app/www/public/ws.php(22): PwgServer-&gt;run()
#6 {main}
  thrown in <b>/config/www/plugins/flickr2piwigo/vendor/samwilson/phpflickr/src/PhotosApi.php</b> on line <b>477</b><br />

[samwilson]

This looks good, thanks! I think getSets() is supposed to be replaced at some point, but this is probably sensible in the meantime. c.f. #14