CreateDynamicBasemapGallery unhandled exception

[williambohrmann3]

Description

If a basemap is not selected and user tries to load, an unhandled exception occurs. Simply return if null. Note this change is included in #1496 for .NET MAUI.

Type of change

• Bug fix

Platforms tested on

• WPF .NET 8
• WPF Framework
• WinUI

Checklist

• Self-review of changes
• All changes work as expected on all affected platforms
• There are no warnings related to changes
• Code is commented and follows .NET conventions and standards
• Codemaid and XAML styler extensions have been run on every changed file
• No unrelated changes have been made to any other code or project files