Never getting None from proc_macro::Span::join

[dtolnay]

This doesn't look right -- both sides of the comparison use self.0.lo().

rust/src/libproc_macro/lib.rs

Lines 248 to 252 in 0f4ebf9

	pub fn join(&self, other: Span) -> Option<Span> {
	let self_loc = __internal::lookup_char_pos(self.0.lo());
	let other_loc = __internal::lookup_char_pos(self.0.lo());
	if self_loc.file.name != other_loc.file.name { return None }

Mentioning @abonander, mentioning #38356

[estebank]

the second lookup should probably be other.0.lo() ^_^