increase stroke preview pad, fix message box capture behavior

src/node_message_box.cpp

@@ -22,6 +22,7 @@ void NodeMessageBox::init()
     btn_ok->on_click = [&](Node*) { destroy(); };
     btn_cancel = m_template->find<NodeButton>("btn-cancel");
     on_submit = btn_cancel->on_click = [&](Node*) { destroy(); };
+    m_capture_children = false; // don't capture children events on mouse_capture
 }
 
 kEventResult NodeMessageBox::handle_event(Event* e)
@@ -44,3 +45,9 @@ kEventResult NodeMessageBox::handle_event(Event* e)
     }
     return kEventResult::Consumed;
 }
+
+void NodeMessageBox::added(Node* parent)
+{
+    Node::added(parent);
+    mouse_capture();
+}