resources/images: Make the image cache more robust

Also allow timeout to be set as a duration string, e.g. `30s`.

Fixes #6501

resources/image_cache.go

@@ -96,12 +96,18 @@ func (c *imageCache) getOrCreate(
 	// These funcs are protected by a named lock.
 	// read clones the parent to its new name and copies
 	// the content to the destinations.
-	read := func(info filecache.ItemInfo, r io.Reader) error {
+	read := func(info filecache.ItemInfo, r io.ReadSeeker) error {
 		img = parent.clone(nil)
 		rp := img.getResourcePaths()
 		rp.relTargetDirFile.file = relTarget.file
 		img.setSourceFilename(info.Name)
 
+		if err := img.InitConfig(r); err != nil {
+			return err
+		}
+
+		r.Seek(0, 0)
+
 		w, err := img.openDestinationsForWriting()
 		if err != nil {
 			return err
@@ -114,6 +120,7 @@ func (c *imageCache) getOrCreate(
 
 		defer w.Close()
 		_, err = io.Copy(w, r)
+
 		return err
 	}