message: Assume room should be unencrypted if homeserver does not implement keys/query
  Dendrite (and others) do not support key fetching (or indeed, E2E at all). Rather than failing to create a room at all, leave it unencrypted. Fixes
diff: @@ -212,7 +212,17 @@ export async function _waitForMember(client, roomId, userId, opts = { timeout: 1
  * can encrypt to.
  */
  export async function canEncryptToAllUsers(client, userIds) {
  - const usersDeviceMap = await client.downloadKeys(userIds);
  + let usersDeviceMap;
  + try {
  + usersDeviceMap = await client.downloadKeys(userIds);
  + } catch (ex) {
  + if (ex.httpStatus === 404) {
  + // The endpoint to fetch keys doesn't exist: force unencrypted.
  + // See: https://github.com/vector-im/riot-web/issues/13598
  + return false;
  + }
  + throw ex;
  + }
  // { "@user:host": { "DEVICE": {...}, ... }, ... }
  return Object.values(usersDeviceMap).every((userDevices) =>
  // { "DEVICE": {...}, ... }
  