Avoid TypeError if resp is undefined

When `resp` is undefined, this error handling code will itself throw "TypeError: Cannot read properties of undefined (reading 'insertErrors')"

Instead of throwing, we can use optional chaining to allow the error message to be handled as expected.

src/rowQueue.ts

@@ -168,7 +168,7 @@ export class RowQueue {
         json,
       },
       (err, resp) => {
-        const partialFailures = (resp.insertErrors || []).map(
+        const partialFailures = (resp?.insertErrors || []).map(
           (insertError: GoogleErrorBody) => {
             return {
               errors: insertError.errors!.map(error => {