Description

I've identified a UI bug in the model visualizer's node styling functionality. When users click the "Style nodes with custom rules" palette button multiple times, the application creates multiple dialog instances instead of maintaining a single dialog.

Current Behavior

When clicking the palette button multiple times:

• Each click creates a new Node Styler dialog
• Multiple dialogs stack on top of each other
• No check is performed to prevent duplicate dialogs
• This creates a confusing user experience and potentially impacts performance

Expected Behavior

• Only one Node Styler dialog should be visible at any time
• Subsequent clicks on the palette button while a dialog is open should not create new dialogs
• The dialog should maintain its state between clicks

Steps to Reproduce

1. Open the model visualizer
2. Locate the palette button (Style nodes with custom rules) in the top right corner
3. Click the button multiple times in succession
4. Observe multiple identical dialogs appearing