Implement ImGuiMouseCursor_NotAllowed mouse cursor.

examples/imgui_impl_win32.cpp

@@ -120,6 +120,7 @@ static bool ImGui_ImplWin32_UpdateMouseCursor()
         case ImGuiMouseCursor_ResizeNESW:   win32_cursor = IDC_SIZENESW; break;
         case ImGuiMouseCursor_ResizeNWSE:   win32_cursor = IDC_SIZENWSE; break;
         case ImGuiMouseCursor_Hand:         win32_cursor = IDC_HAND; break;
+        case ImGuiMouseCursor_NotAllowed:   win32_cursor = IDC_NO; break;
         }
         ::SetCursor(::LoadCursor(NULL, win32_cursor));
     }