fix(textarea): modelValue 值为`null`时的`length`引用错误 (#805)

src/packages/__VUE/textarea/index.taro.vue

@@ -18,7 +18,7 @@
       :placeholder="placeholder"
     />
     <view class="nut-textarea__limit" v-if="limitShow">
-      {{ modelValue.length }}/{{ maxLength }}</view
+      {{ modelValue ? modelValue.length : 0 }}/{{ maxLength }}</view
     >
   </view>
 </template>

src/packages/__VUE/textarea/index.vue

@@ -14,7 +14,7 @@
       :placeholder="placeholder"
     />
     <view class="nut-textarea__limit" v-if="limitShow">
-      {{ modelValue.length }}/{{ maxLength }}</view
+      {{ modelValue ? modelValue.length : 0 }}/{{ maxLength }}</view
     >
   </view>
 </template>