Don't fatal when calling expect_one_of when recovering arg in parse_seq

tests/ui/impl-trait/precise-capturing/unexpected-token.rs

@@ -0,0 +1,9 @@
+// We used to fatal error without any useful diagnostic when we had an unexpected
+// token due to a strange interaction between the sequence parsing code and the
+// param/lifetime parsing code.
+
+fn hello() -> impl use<'a {}> Sized {}
+//~^ ERROR expected one of `,` or `>`, found `{`
+//~| ERROR expected item, found `>`
+
+fn main() {}