Make UBP nil/count checks debug-mode only
Make UBP nil/count checks debug-mode only

Every other Unsafe(Mutable)BufferPointer precondition in this file is debug-mode only.

This information is already part of the documentation for this function, and it's really hard to get rid of these branches and traps otherwise.
benlangmuir/swift,jmgc/swift,xwu/swift,apple/swift,atrick/swift,gregomni/swift,atrick/swift,tkremenek/swift,parkera/swift,ahoppen/swift,jmgc/swift,xwu/swift,ahoppen/swift,glessard/swift,benlangmuir/swift,parkera/swift,rudkx/swift,gregomni/swift,hooman/swift,ahoppen/swift,parkera/swift,parkera/swift,hooman/swift,JGiola/swift,atrick/swift,glessard/swift,tkremenek/swift,jmgc/swift,tkremenek/swift,xwu/swift,JGiola/swift,rudkx/swift,gregomni/swift,roambotics/swift,rudkx/swift,JGiola/swift,ahoppen/swift,jmgc/swift,apple/swift,JGiola/swift,atrick/swift,gregomni/swift,atrick/swift,apple/swift,gregomni/swift,apple/swift,roambotics/swift,jmgc/swift,benlangmuir/swift,jmgc/swift,roambotics/swift,atrick/swift,JGiola/swift,hooman/swift,xwu/swift,gregomni/swift,benlangmuir/swift,ahoppen/swift,roambotics/swift,apple/swift,glessard/swift,parkera/swift,benlangmuir/swift,xwu/swift,tkremenek/swift,ahoppen/swift,tkremenek/swift,parkera/swift,tkremenek/swift,rudkx/swift,rudkx/swift,hooman/swift,roambotics/swift,tkremenek/swift,jmgc/swift,roambotics/swift,glessard/swift,rudkx/swift,xwu/swift,hooman/swift,glessard/swift,apple/swift,benlangmuir/swift,glessard/swift,hooman/swift,parkera/swift,hooman/swift,parkera/swift,xwu/swift,JGiola/swift