Postpone setting the brand color until soapbox.json succeeds or fails

Fixes color flickering during load

app/soapbox/containers/soapbox.js

@@ -48,7 +48,7 @@ const mapStateToProps = (state) => {
     dyslexicFont: settings.get('dyslexicFont'),
     demetricator: settings.get('demetricator'),
     locale: settings.get('locale'),
-    themeCss: generateThemeCss(state.getIn(['soapbox', 'brandColor'], '#0482d8')), // Azure default
+    themeCss: generateThemeCss(state.getIn(['soapbox', 'brandColor'])),
     themeMode: settings.get('themeMode'),
   };
 };

app/soapbox/reducers/soapbox.js

@@ -1,12 +1,21 @@
-import { SOAPBOX_CONFIG_REQUEST_SUCCESS } from '../actions/soapbox';
+import {
+  SOAPBOX_CONFIG_REQUEST_SUCCESS,
+  SOAPBOX_CONFIG_REQUEST_FAIL,
+} from '../actions/soapbox';
 import { Map as ImmutableMap, fromJS } from 'immutable';
 
 const initialState = ImmutableMap();
 
+const defaultState = ImmutableMap({
+  brandColor: '#0482d8', // Azure
+});
+
 export default function soapbox(state = initialState, action) {
   switch(action.type) {
   case SOAPBOX_CONFIG_REQUEST_SUCCESS:
-    return ImmutableMap(fromJS(action.soapboxConfig));
+    return defaultState.merge(ImmutableMap(fromJS(action.soapboxConfig)));
+  case SOAPBOX_CONFIG_REQUEST_FAIL:
+    return defaultState;
   default:
     return state;
   }