fix(savegame): fix savefiles directory not being created (#5917)

A refactor of the load/save UI in commit
7b6a797 introduced a bug preventing the
"savefiles" directory from getting created, and causing an error-popup
whenever the directory was attempted to be accessed by the LUA UI.

The bug was resetting a variable to an unexpected value which then
caused the "sort" algorithm to throw an error. This was resolved by
ensuring that the variable always had a valid value for the sort
algorithm.

data/pigui/modules/saveloadgame.lua

@@ -274,10 +274,10 @@ function SaveLoadWindow:makeFileList()
 	if not ok then
 		Notification.add(Notification.Type.Error, lui.COULD_NOT_LOAD_SAVE_FILES, files --[[@as string]])
 		self.files = {}
+	else
+		self.files = files
 	end
 
-	self.files = files
-
 	table.sort(self.files, function(a, b)
 		return a.mtime.timestamp > b.mtime.timestamp
 	end)