fix(theme): language menu undefined text (#2755)

Co-authored-by: 三咲智子 Kevin Deng <sxzz@sxzz.moe>

src/client/theme-default/components/VPFlyout.vue

@@ -39,7 +39,7 @@ function onBlur() {
     >
       <span v-if="button || icon" class="text">
         <component v-if="icon" :is="icon" class="option-icon" />
-        <span v-html="button"></span>
+        <span v-if="button" v-html="button"></span>
         <VPIconChevronDown class="text-icon" />
       </span>