Add extra check for missing sourcemap files

Author: Alexis Pierru

main.ts

@@ -75,6 +75,10 @@ async function run() {
     form.append("file", fs.createReadStream(file_path));
 
     if (sourcemap_file_path) {
+      if (!fs.existsSync(sourcemap_file_path)) {
+        throw new Error("Could not access file:" + sourcemap_file_path);
+      }
+
       try {
         form.append("sourcemap", fs.createReadStream(sourcemap_file_path));
       } catch (err) {