fix image serving performance problem introduced in last release.

go/weed/weed_server/volume_server_handlers.go

@@ -125,7 +125,6 @@ func (vs *VolumeServer) GetOrHeadHandler(w http.ResponseWriter, r *http.Request,
 		}
 	}
 	if ext == ".png" || ext == ".jpg" || ext == ".gif" {
-		if srcImage, _, err := image.Decode(bytes.NewReader(n.Data)); err == nil {
 		width, height := 0, 0
 		if r.FormValue("width") != "" {
 			width, _ = strconv.Atoi(r.FormValue("width"))
@@ -134,6 +133,7 @@ func (vs *VolumeServer) GetOrHeadHandler(w http.ResponseWriter, r *http.Request,
 			height, _ = strconv.Atoi(r.FormValue("height"))
 		}
 		if width != 0 || height != 0 {
+			if srcImage, _, err := image.Decode(bytes.NewReader(n.Data)); err == nil {
 				bounds := srcImage.Bounds()
 				var dstImage *image.NRGBA
 				if width == height && bounds.Dx() != bounds.Dy() {