Potential bug - "Error Occured" on convert to order

Left this at the simplest "fix": handle the exception.

I’m assigning this back to Josh, given that he’s back. (Yay!)

Beginning to get ramped up on this resulted in:

• https://openlmis.atlassian.net/browse/OLMIS-145

• The exceedingly simple pull-request at https://github.com/OpenLMIS/open-lmis/pull/99. I used a pull-request because I’m not ultimately certain that the added checks are necessary. Specifically, I’m not sure what the delta is between our test/demo seed data and how we expect new users to configure a system. With our current test/demo seed data, however, the checks in this pull-request made for a more robust system.

This does seem to be an exception in sending emails, which doesn't seem like it should be a problem. Not sure what change caused this. Oddly it seems that RNR status changes RequistionService.sendRequistionsStatusChangeMail is no longer being called while the order change service still is. I'd like to track down why this change occurred and if it's leading to the issue where the flag to send mail is set for the supply depot...

I didn't have the time to track down the root change here or untagle the above question about no longer sending emails on RNR status changes. Throwing back in pool as I'll be OOF.