fix

weed/images/resizing.go

@@ -19,11 +19,18 @@ func Resized(ext string, data []byte, width, height int) (resized []byte, w int,
 
 	dx := srcImage.Bounds().Dx()
 	dy := srcImage.Bounds().Dy()
+
+	if height == 0 {
+		height = width * dy / dx
+	} else if width == 0 {
+		width = height * dx / dy
+	} else {
 		if width/height > dx/dy { //定高
 			width = height * dx / dy
 		} else if width/height < dx/dy { //定宽
 			height = width * dy / dx
 		}
+	}
 
 	if err == nil {
 		bounds := srcImage.Bounds()