[webview] prevent potential double resolution in XMLHttpRequest handling (#22404)

Although the JavaScript engine can handle this situation, attempting to
handle both `resolve` and `reject` for the same `Promise` in the code
logic indicates that the code structure is not sufficiently rigorous and
may have design flaws. This can obscure the intent of the code and
potentially confuse other developers.

Author: 0xlau

src/web_or_worker_shell_read.js

@@ -30,6 +30,7 @@
         xhr.onload = () => {
           if (xhr.status == 200 || (xhr.status == 0 && xhr.response)) { // file URLs can return 0
             resolve(xhr.response);
+            return;
           }
           reject(xhr.status);
         };