When creating raid5 or striped plexes, avoid falling out of bounds when checking the given stripe size.
When creating raid5 or striped plexes, avoid falling out of bounds
when checking the given stripe size.

Also move the code a bit around to avoid duplication.

Approved by: joerg (mentor)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase