Fix panic double clicking on debugger resize handle (#30569)

Closes #ISSUE

Co-Authored-By: Cole <cole@zed.dev>

Release Notes:

- N/A

crates/debugger_ui/src/debugger_panel.rs

@@ -1119,7 +1119,7 @@ impl Panel for DebugPanel {
     }
 
     fn set_size(&mut self, size: Option<Pixels>, _window: &mut Window, _cx: &mut Context<Self>) {
-        self.size = size.unwrap();
+        self.size = size.unwrap_or(px(300.));
     }
 
     fn remote_id() -> Option<proto::PanelId> {