bug#40010: 27.0.90; fix: Specify xlink namespace for svg images

[Zhu Zihao]

svg-create in svg.el generates a svg without specifying the namespace of xlink.
This may fails the render of a svg with image embed in.

A SVG example failed to render was provided here: https://pastebin.com/9QnuMy7Y.

IMO this patch can help fix this issue.

~~~~~~~~

From 93188f91906dea87bfbf62e18b608bbd2f84c7af Mon Sep 17 00:00:00 2001
From: Zhu Zihao <all_but_last@163.com>
Date: Tue, 10 Mar 2020 19:46:03 +0800
Subject: [PATCH] fix: Specify xlink namespace for svg images.

---
 lisp/svg.el | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lisp/svg.el b/lisp/svg.el
index 6a2fc4c90fc..370c9c04e76 100644
--- a/lisp/svg.el
+++ b/lisp/svg.el
@@ -70,7 +70,8 @@ svg-create
              (height . ,height)
              (version . "1.1")
              (xmlns . "http://www.w3.org/2000/svg";)
-             ,@(svg--arguments nil args))))
+              (xmlns:xlink . "http://www.w3.org/1999/xlink";)
+              ,@(svg--arguments nil args))))
 
 (defun svg-gradient (svg id type stops)
   "Add a gradient with ID to SVG.
-- 
2.25.1