Add verification of number of items in the table to prevent editing an empty object with no index

src/main.py

@@ -123,9 +123,10 @@ class MedTrackerApp:
 
     def on_double_click(self, event):
         """Handle double-click event to edit an entry."""
-        item_id = self.tree.selection()[0]
-        item_values = self.tree.item(item_id, "values")
-        self.create_edit_window(item_id, item_values)
+        if len(self.tree.get_children()) > 0:
+            item_id = self.tree.selection()[0]
+            item_values = self.tree.item(item_id, "values")
+            self.create_edit_window(item_id, item_values)
 
     def create_edit_window(self, item_id, values):
         """Create a new Toplevel window for editing an entry."""