improve robustness of appearance tab

src/components/settings_modal/tabs/appearance_tab.js

@@ -119,7 +119,16 @@ const AppearanceTab = {
 
     updateIndex('theme').then(themes => {
       themes.forEach(([key, themePromise]) => themePromise.then(data => {
-        this.availableThemesV2.push({ key, data, name: data.name, version: 'v2' })
+        console.log('DEBUG', data)
+        if (!data) {
+          console.warn(`Theme with key ${key} is empty or malformed`)
+        } else if (Array.isArray(data)) {
+          console.warn(`Theme with key ${key} is a v1 theme and should be moved to static/palettes/index.json`)
+        } else if (!data.source && !data.theme) {
+          console.warn(`Theme with key ${key} is malformed`)
+        } else {
+          this.availableThemesV2.push({ key, data, name: data.name, version: 'v2' })
+        }
       }))
     })
 

src/components/settings_modal/tabs/theme_tab/theme_tab.js

@@ -133,7 +133,7 @@ export default {
       Object
         .values(themesIndex)
         .forEach(themeFunc => {
-          themeFunc().then(themeData => this.availableStyles.push(themeData))
+          themeFunc().then(themeData => themeData && this.availableStyles.push(themeData))
         })
     })
   },