RiverCode, ReachCode check before SDF creation

[erpas]

HEC-RAS import tool doesn't accept reaches with identical river and reach code. If there are few reaches in the geometry and user did not specify unique codes for them, the SDF is created successfully but HEC-RAS won't get them because they all have None-None as river and reach code.

We should check the codes before creating SDF or, ideally, somewhat earlier, say at network topology creation. That would save as from troubles later.