fix(Combobox,Listbox): handle empty option groups and null element refs

Author: bnjm

src/components/Combobox.vue

@@ -126,7 +126,7 @@ const container = ref()
 const query = ref('')
 const inputRef = ref()
 const comboboxButton = ref()
-const optionsPanelWidth = computed(() => comboboxButton.value?.el.offsetWidth)
+const optionsPanelWidth = computed(() => comboboxButton.value?.el?.offsetWidth)
 
 const selectInputValue = () => {
   if (inputRef.value) {

src/components/Listbox.vue

@@ -82,7 +82,7 @@ const emit = defineEmits<{
 const attrs = useAttrs()
 
 const listboxButton = ref()
-const optionsPanelWidth = computed(() => listboxButton.value?.el.offsetWidth)
+const optionsPanelWidth = computed(() => listboxButton.value?.el?.offsetWidth)
 
 // hack together a tab-out behavior for the listbox
 const handleTab = (event: KeyboardEvent) => {