fix(nc-gui): prevent gallery cover img error

packages/nc-gui/components/smartsheet/Gallery.vue

@@ -177,7 +177,7 @@ watch(view, async (nextView) => {
             class="!rounded-lg h-full overflow-hidden break-all max-w-[450px]"
             @click="expandFormClick($event, record)"
           >
-            <template v-if="galleryData.fk_cover_image_col_id" #cover>
+            <template v-if="galleryData?.fk_cover_image_col_id" #cover>
               <a-carousel v-if="!reloadAttachments && attachments(record).length" autoplay class="gallery-carousel" arrows>
                 <template #customPaging>
                   <a>