Harden suspense image preload cache handling

Co-authored-by: Kent C. Dodds <me+github@kentcdodds.com>

Author: cursoragent

app/utils/suspense-image.ts

@@ -25,12 +25,19 @@ function preloadImage(src: string) {
 	// SSR-safe: callers should generally only use this in the browser, but guard
 	// anyway so we never throw on `new Image()` during server rendering.
 	if (typeof Image === 'undefined') return Promise.resolve(src)
+	if (!src) return Promise.resolve(src)
 
 	return new Promise<string>((resolve, reject) => {
 		const img = new Image()
-		img.src = src
 		img.onload = () => resolve(src)
 		img.onerror = reject
+		img.src = src
+
+		// If the image is already in cache, `complete` can be true immediately.
+		if (img.complete) {
+			if (img.naturalWidth > 0) resolve(src)
+			else reject(new Error(`Failed to preload image: ${src}`))
+		}
 	})
 }