Fix missing image download button (#30320)

Fixes #30319

(cherry picked from commit 114ad1d)

Author: dbkr

src/components/views/elements/ImageView.tsx

@@ -620,6 +620,8 @@ function DownloadButton({
                     // Err on the side of safety.
                     setCanDownload(false);
                 });
+        } else {
+            setCanDownload(true);
         }
     }, [mxEvent]);