Don't panic when multiple Zed instances are open (#10295)

This stops an annoying panic that can occur when developing Zed 

Release Notes:

- N/A

crates/workspace/src/persistence.rs

@@ -352,8 +352,7 @@ impl WorkspaceDb {
                 // Clear out panes and pane_groups
                 conn.exec_bound(sql!(
                     DELETE FROM pane_groups WHERE workspace_id = ?1;
-                    DELETE FROM panes WHERE workspace_id = ?1;))?(workspace.id)
-                .expect("Clearing old panes");
+                    DELETE FROM panes WHERE workspace_id = ?1;))?(workspace.id)?;
 
                 conn.exec_bound(sql!(
                     DELETE FROM workspaces WHERE workspace_location = ? AND workspace_id != ?