"Open World" dialog does not open if the saves folder does not exist

[dkluin]

Describe the bug
When attempting to open a world folder, the saves folder must exist for the file dialog to open. If it isn't, nothing will happen.

To Reproduce
Steps to reproduce the behavior:

1. Install a clean version of MCA whilst making sure all settings are set to default.
2. Go to Settings
3. Set the saves directory to a random string (doesn't matter what, as long as it isn't a valid path)
4. Click OK
5. Go to File -> Open World.

Nothing will happen next.

Expected behavior
When starting MCA, the user should be given a warning informing him that the saves directory (as specified in the settings page) does not exist. There should also be an additional check when trying to change the saves directory to validate the entered folder path. Both of these changes should ensure the bug no longer occurs.

Screenshots and other files
None are applicable. Simply follow the steps provided above to replicate the issue.

Environment (please complete the following information):

• OS: Windows 11
• Java version: I have both Java 8 update 401 and JDK 18.0.2.1 installed.
• Version of MCA Selector: 2.3

Additional context
N/A