web/elements: fix TokenCopyButton error case

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

web/src/elements/buttons/TokenCopyButton.ts

@@ -30,9 +30,9 @@ export class TokenCopyButton extends ActionButton {
                 }, 1500);
             });
         }).catch((err: Response) => {
-            return err.json();
+            return err.json().then(errResp => {
-        }).then(errResp => {
+                throw new Error(errResp["detail"]);
-            throw new Error(errResp["detail"]);
+            });
         });
     }