JS: protect against null EventHandles in killEvent and interruptEvent
JS: protect against null EventHandles in killEvent and interruptEvent

It is easy to protect against a null pointer here, do so after checking we are
in a Process context, so that we always fail if called in a bad context.

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

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