Textarea: fix undefined in ssr when v-model not set (#10630)

packages/input/src/input.vue

@@ -121,7 +121,7 @@
 
     data() {
       return {
-        currentValue: this.value,
+        currentValue: this.value || '',
         textareaCalcStyle: {},
         prefixOffset: null,
         suffixOffset: null,