Show server details on login for unreachable homeserver

This fixes the login page to be more helpful when the current homeserver is
unreachable: it reveals the server change field, so you have some chance to
progress forward.

Fixes https://github.com/vector-im/riot-web/issues/11077

src/components/structures/auth/Login.js

@@ -386,7 +386,11 @@ module.exports = createReactClass({
                 ...AutoDiscoveryUtils.authComponentStateForError(e),
             });
             if (this.state.serverErrorIsFatal) {
-                return; // Server is dead - do not continue.
+                // Server is dead: show server details prompt instead
+                this.setState({
+                    phase: PHASE_SERVER_DETAILS,
+                });
+                return;
             }
         }