fix: spa mode

Author: hamsoover

lib/templates/plugin.client.js

@@ -8,7 +8,7 @@ const colorMode = window['<%= options.globalName %>']
 const getForcedColorMode = route => route.matched[0] && route.matched[0].components.default.options.colorMode
 
 export default function (ctx, inject) {
-  let data = ctx.nuxtState.colorMode
+  let data = ctx.nuxtState ? ctx.nuxtState.colorMode : null
   // For SPA mode or fallback
   if (!data) {
     data = {