Fix crash when script throws non-error object

lib/sandbox.js

@@ -243,18 +243,25 @@ function errorToFault(err) {
   if (!err)
     return null;
 
-  // Trim the stack trace at the self-executing anonymous wrapper function
-  let stackTrimIndex = err.stack.match(/\s+at\s[^\s]+\s+at\s[^\s]+\s\(vm\.js.+\)/).index;
+  if (!err.name)
+    return {code: "script", message: `${err}`};
 
-  return {
+  let fault = {
     code: `script.${err.name}`,
     message: err.message,
     detail: {
       name: err.name,
-      message: err.message,
-      stack: err.stack.slice(0, stackTrimIndex)
+      message: err.message
     }
+  };
+
+  if (err.stack) {
+    // Trim the stack trace at the self-executing anonymous wrapper function
+    let stackTrimIndex = err.stack.match(/\s+at\s[^\s]+\s+at\s[^\s]+\s\(vm\.js.+\)/).index;
+    fault.detail.stack = err.stack.slice(0, stackTrimIndex);
   }
+
+  return fault;
 }