Fix: Kots with product quantity = 0 were allowed. So blank kots could be added.

bookie/src/app/sales/bill.service.ts

@@ -237,7 +237,7 @@ export class BillService {
   printKot(guestBookId: string | null): Observable<boolean> {
     const item = JSON.parse(JSON.stringify(this.bill));
     const newKot = this.bill.kots.find((k) => k.id === undefined) as Kot;
-    if (newKot.inventories.length === 0) {
+    if (newKot.inventories.filter((x) => x.quantity !== 0).length === 0) {
       return throwError('Cannot print a blank KOT\nPlease add some products!');
     }
     if (!this.happyHourItemsBalanced() || this.happyHourItemsMoreThanRegular()) {