Do not ICE on unicode next point

Use `shrink_to_hi` instead of `next_point`
Fix rust-lang#68000.

(cherry picked from commit fcd850f)

Author: estebank

src/librustc_parse/parser/item.rs

@@ -1572,7 +1572,7 @@ impl<'a> Parser<'a> {
                 }
             }
             _ => {
-                let sp = self.sess.source_map().next_point(self.prev_span);
+                let sp = self.prev_span.shrink_to_hi();
                 let mut err = self.struct_span_err(sp, &format!("expected `,`, or `}}`, found {}",
                                                                 self.this_token_descr()));
                 if self.token.is_ident() {

src/test/ui/issues/issue-68000-unicode-ident-after-missing-comma.rs

@@ -0,0 +1,6 @@
+pub struct Foo {
+    pub bar: Vec<i32>ö
+    //~^ ERROR expected `,`, or `}`, found `ö`
+} //~ ERROR expected `:`, found `}`
+
+fn main() {}

src/test/ui/issues/issue-68000-unicode-ident-after-missing-comma.stderr

@@ -0,0 +1,17 @@
+error: expected `,`, or `}`, found `ö`
+  --> $DIR/issue-68000-unicode-ident-after-missing-comma.rs:2:22
+   |
+LL |     pub bar: Vec<i32>ö
+   |                      ^ help: try adding a comma: `,`
+
+error: expected `:`, found `}`
+  --> $DIR/issue-68000-unicode-ident-after-missing-comma.rs:4:1
+   |
+LL |     pub bar: Vec<i32>ö
+   |                       - expected `:`
+LL |
+LL | }
+   | ^ unexpected token
+
+error: aborting due to 2 previous errors
+