Keep sign in button disabled on success

This changes password login to keep the sign in button locked when proceeding
successfully to avoid the possibility of double device sign in.

Part of https://github.com/vector-im/riot-web/issues/12546

src/components/structures/auth/Login.js

@@ -245,6 +245,7 @@ export default createReactClass({
             }
 
             this.setState({
+                busy: false,
                 errorText: errorText,
                 // 401 would be the sensible status code for 'incorrect password'
                 // but the login API gives a 403 https://matrix.org/jira/browse/SYN-744
@@ -252,13 +253,6 @@ export default createReactClass({
                 // We treat both as an incorrect password
                 loginIncorrect: error.httpStatus === 401 || error.httpStatus === 403,
             });
-        }).finally(() => {
-            if (this._unmounted) {
-                return;
-            }
-            this.setState({
-                busy: false,
-            });
         });
     },