go: remove ineff assignment, add missing err check

Signed-off-by: Paul Meyer <49727155+katexochen@users.noreply.github.com>

cmd/cmd.go

@@ -41,7 +41,9 @@ func (c *Config) FromFlags(fs *flag.FlagSet) {
 	}
 
 	fs.StringVar(&c.id, "id", "keep-sorted", "The identifier used to enable this tool in files.")
-	fs.MarkHidden("id")
+	if err := fs.MarkHidden("id"); err != nil {
+		panic(err)
+	}
 
 	of := &operationFlag{op: &c.operation}
 	if err := of.Set("fix"); err != nil {
@@ -147,7 +149,7 @@ func (f *lineRangeFlag) parse(vals []string) ([]keepsorted.LineRange, error) {
 		if err != nil {
 			return nil, fmt.Errorf("invalid line range %q: %w", val, err)
 		}
-		end := -1
+		var end int
 		if len(sp) == 1 {
 			end = start
 		} else {