Do not ICE on unicode next point

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

src/librustc_parse/parser/item.rs

@@ -1489,7 +1489,7 @@ 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 {}", super::token_descr(&self.token)),

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
+