[ticket/11404] Return empty array of avatar data if $row is empty

While creating a group in the acp, the group data ($group_row) is empty.
Due to that array_combine in phpbb_avatar_manager::clean_row() will cause
PHP Warnings. In addition to that the required indexes 'avatar',
'avatar_width', 'avatar_height', and 'avatar_type' won't be defined. This
patch will solve that issue.

PHPBB3-11404

phpBB/includes/avatar/manager.php

@@ -177,6 +177,17 @@ class phpbb_avatar_manager
 		$keys = array_keys($row);
 		$values = array_values($row);
 
+		// Upon creation of a user/group $row might be empty
+		if (empty($keys))
+		{
+			return array(
+				'avatar'		=> '',
+				'avatar_type'	=> '',
+				'avatar_width'	=> '',
+				'avatar_height'	=> '',
+			);
+		}
+
 		$keys = array_map(array('phpbb_avatar_manager', 'strip_prefix'), $keys);
 
 		return array_combine($keys, $values);