fix(purchase-reco): use optional chaining for message handling in download_gstr function

(cherry picked from commit b4c165c)

Author: karm1000

india_compliance/gst_india/doctype/purchase_reconciliation_tool/purchase_reconciliation_tool.js

@@ -1225,10 +1225,10 @@ async function download_gstr(
         frm.events.show_progress(frm, "download");
         const { message } = await frm.taxpayer_api_call("download_gstr", args);
 
-        if (message.message) {
+        if (message?.message) {
             frappe.show_alert({
                 message: message.message,
-                indicator: message.indicator || "blue",
+                indicator: message?.indicator || "blue",
             });
         }
     });