JS: fix bug in 'getEntityReference' for ExpressionBox
JS: fix bug in 'getEntityReference' for ExpressionBox

Always finds the entity referenced in an expression under construction.

Signed-off-by: Harry King <409587b9e6671aa0763646191d292852dc49a658@gmail.com>

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