[InstCombine] Transform !range metadata to !nonnull when combining loads

When combining an integer load with !range metadata that does not include 0 to a pointer load, make sure emit !nonnull metadata on the newly-created pointer load. This prevents the !nonnull metadata from being dropped during a ptrtoint/inttoptr pair.

This fixes PR30597.

Patch by Ariel Ben-Yehuda!

Differential Revision: https://reviews.llvm.org/D25215

llvm-svn: 283836