JS: reduce the amount of queue callbacks when multiple elements added concurrently
JS: reduce the amount of queue callbacks when multiple elements added concurrently

If we are already scheduled to run the QueueUser callbacks, don't bother scheduleing
another, we can rely on the first one.

Signed-off-by: Harvey Harrison <eadbd6b462bf3c97df0300a934c12bc2e5d1fe51@ausenco.com>

jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim