[backport core/1.34] fix: refreshing assets causes entire panel to re-render (enter loading state) (#7526)

Backport of #7449 to core/1.34.

## Original PR
https://github.com/Comfy-Org/ComfyUI_frontend/pull/7449

## Changes
- Only show loading spinner when `loading && !displayAssets.length`
instead of just `loading`
- Prevents jarring re-render when refreshing assets

src/components/sidebar/tabs/AssetsSidebarTab.vue

@@ -48,12 +48,11 @@
       />
     </template>
     <template #body>
-      <!-- Loading state -->
-      <div v-if="loading">
+      <Divider type="dashed" class="m-2" />
+      <div v-if="loading && !displayAssets.length">
         <ProgressSpinner class="absolute left-1/2 w-[50px] -translate-x-1/2" />
       </div>
-      <!-- Empty state -->
-      <div v-else-if="!displayAssets.length">
+      <div v-else-if="!loading && !displayAssets.length">
         <NoResultsPlaceholder
           icon="pi pi-info-circle"
           :title="
@@ -66,7 +65,6 @@
           :message="$t('sideToolbar.noFilesFoundMessage')"
         />
       </div>
-      <!-- Content -->
       <div v-else class="relative size-full" @click="handleEmptySpaceClick">
         <VirtualGrid
           :items="mediaAssetsWithKey"
@@ -167,6 +165,7 @@
 
 <script setup lang="ts">
 import { useDebounceFn, useElementHover, useResizeObserver } from '@vueuse/core'
+import { Divider } from 'primevue'
 import ProgressSpinner from 'primevue/progressspinner'
 import { useToast } from 'primevue/usetoast'
 import { computed, onMounted, onUnmounted, ref, watch } from 'vue'