refactor: remove unneeded isset($config) check

Author: kenjis

system/Database/Config.php

@@ -65,18 +65,12 @@ public static function connect($group = null, bool $getShared = true)
             if (! isset($dbConfig->{$group})) {
                 throw new InvalidArgumentException($group . ' is not a valid database connection group.');
             }
-        }
 
-        if ($getShared && isset(static::$instances[$group])) {
-            return static::$instances[$group];
-        }
-
-        if (isset($dbConfig->{$group})) {
             $config = $dbConfig->{$group};
         }
 
-        if (! isset($config)) {
-            throw new InvalidArgumentException('There is no valid database config.');
+        if ($getShared && isset(static::$instances[$group])) {
+            return static::$instances[$group];
         }
 
         static::ensureFactory();