Handle INCX=0,INCY=0 case
Handle INCX=0,INCY=0 case

Fixes #1575 (sswap/dswap failing the swap utest on x86) as suggested by atsampson.
xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS