Disable mouse popup for empty space in map selection window

[ihhub]

Preliminary checks

• [X] I've checked that there aren't other open issues on the same topic.

Describe the problem requiring a solution

This is how it looks when not enough maps exist in the list:

https://github.com/ihhub/fheroes2/assets/19829520/9ba03ac6-fbf1-4fc3-aa87-5e4168d74e54

Describe the possible solution

Do not show this popup dialog if a user is clicking on an empty space.

Additional info

No response

[oleg-derevenetz]

Closed by #9001.