Fix another off-by-one in bounds check of fetchmem
Fix another off-by-one in bounds check of fetchmem

Yeesh.  This bounds check was one byte too tight, so you fetching
memory that ended at USERTOP-1 would fail.

aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,aclements/sv6