#894 Can't un-destroy missing parts with Edit Damage Dialog

[Taharqa]

If a user uses the edit damage dialog to "un-destroy" a missing part (e.g. removes two out of three hits from a gyro) that missing part is not replaced with a real part, which can cause problems in the repair dialog, plus when the user next saves and loads that part will be destroyed again. I think this could be fixed by applying the updateConditionFromEntity method to missing parts but we want to be careful with that.