Prevent undefined method `split' for nil:NilClass with pe_foo_version facts

Prevent undefined method `split' for nil:NilClass with pe_foo_version facts

Without this patch the pe_major_version, pe_minor_version, and
pe_patch_version facts directly depend on the pe_version fact in a
manner that calls split directly on the return value.

This is a problem because Fact values are not always guaranteed to
return strings, or objects that respond to split.  This patch is a
defensive measure to ensure we're always calling the split method on a
string object.

If the Fact returns nil, this will be converted to an empty string
responding to split.