erp5_open_trade: do not reexpand simulation if there is no simulation movement to create

expand always reindex the full simulation tree, even if there is nothing to do.
This is cpu costly.
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Status Job ID Name Coverage
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passed ERP5.CodingStyleTest-Master

00:46:15

passed ERP5.UnitTest-Master

01:13:00

passed SlapOS.Eggs.UnitTest-Master.Python2

00:13:07

passed SlapOS.Eggs.UnitTest-Master.Python3

00:15:58

passed Wendelin.UnitTest-Master

00:40:15