Fix ICE

Author: sjwang05

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -910,7 +910,10 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         steps -= 1;
                     }
                     if steps == 0 {
-                        msg = msg.trim_end_matches(" and dereferencing instead");
+                        return (
+                            msg.trim_end_matches(" and dereferencing instead"),
+                            vec![(prefix_span, String::new())],
+                        );
                     }
                     let derefs = "*".repeat(steps);
                     let needs_parens = steps > 0
@@ -933,7 +936,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             format!("{derefs}"),
                         )]
                     };
-                    suggestion.push((prefix_span, "".to_string()));
+                    suggestion.push((prefix_span, String::new()));
                     (msg, suggestion)
                 };