[FIX] Do not try to hoist "empty" accesses

  Accesses that have a relative offset (in bytes) that is not divisible
  by the type size (in bytes) will be represented as empty in the SCoP
  description. This is on its own not good but it also crashed the
  invariant load hoisting. This patch will fix the latter problem while
  the former should be addressed too.

  This fixes bug 25236.

llvm-svn: 250664