Replace use of 'array_merge' with the spread operator and 'array_push' in various places.

This isn't supported for arrays with string keys until PHP 8.1.

https://wiki.php.net/rfc/spread_operator_for_array

plugins/af_comics/init.php

@@ -19,7 +19,10 @@ class Af_Comics extends Plugin {
 
 		require_once __DIR__ . "/filter_base.php";
 
-		$filters = array_merge(glob(__DIR__ . "/filters.local/*.php"), glob(__DIR__ . "/filters/*.php"));
+		$filters = [
+			...(glob(__DIR__ . "/filters.local/*.php") ?: []),
+			...(glob(__DIR__ . "/filters/*.php") ?: []),
+		];
 		$names = [];
 
 		foreach ($filters as $file) {