Update Citations.svelte (open-webui#21897)

Add on:error handler to img

Author: fama-05

src/lib/components/chat/Messages/Citations.svelte

@@ -178,6 +178,9 @@
 							src="https://www.google.com/s2/favicons?sz=32&domain={citation.source.name}"
 							alt="favicon"
 							class="size-4 rounded-full shrink-0 border border-white dark:border-gray-850 bg-white dark:bg-gray-900"
+							on:error={(e) => {
+								e.target.src = '/favicon.png';
+							}}
 						/>
 					{/each}
 				</div>