Fix "URI malformed" crashes on Windows

ts/components/CallBackgroundBlur.tsx

@@ -1,4 +1,4 @@
-// Copyright 2020 Signal Messenger, LLC
+// Copyright 2020-2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import React from 'react';
@@ -26,7 +26,7 @@ export const CallBackgroundBlur = ({
         <div
           className="module-calling__background--blur"
           style={{
-            backgroundImage: `url("${avatarPath}")`,
+            backgroundImage: `url('${encodeURI(avatarPath)}')`,
           }}
         />
       )}