Add async custom input component support

fixes #417

Author: kaskar2008

lib/vue-simple-suggest.vue

@@ -221,11 +221,18 @@ export default {
   created () {
     this.controlScheme = Object.assign({}, defaultControls, this.controls)
   },
-  mounted () {
+  async mounted () {
+    await this.$slots.default;
+
     this.inputElement = this.$refs['inputSlot'].querySelector('input')
 
-    this.setInputAriaAttributes()
-    this.prepareEventHandlers(true)
+    if (this.inputElement) {
+
+      this.setInputAriaAttributes()
+      this.prepareEventHandlers(true)
+    } else {
+      console.error('No input element found')
+    }
   },
   beforeDestroy () {
     this.prepareEventHandlers(false)