Don't try to set crypto options without crypto enabled

src/components/structures/MatrixChat.js

@@ -1505,7 +1505,6 @@ export default createReactClass({
                 "blacklistUnverifiedDevices",
             );
             cli.setGlobalBlacklistUnverifiedDevices(blacklistEnabled);
-        }
 
             // With cross-signing enabled, we send to unknown devices
             // without prompting. Any bad-device status the user should
@@ -1515,6 +1514,8 @@ export default createReactClass({
             cli.setGlobalErrorOnUnknownDevices(
                 !SettingsStore.isFeatureEnabled("feature_cross_signing"),
             );
+        }
+
     },
 
     showScreen: function(screen, params) {