Fix compile error CS0165 on Mono

When running on mono building scripts, it will yield

Errors:
 + Engines/BulkOrders/SmallTailorBOD.cs:
     CS0165: Line 88: Use of unassigned local variable `useMaterials'

Calling RandomBool out of if
Merge pull request #2 from fraga/fixCS0165

If it makes Mono happy, why not?

Fix compile error CS0165 on Mono