Prevent creation of 0 gold Letters of Credit

Forums: https://forums.dfworkshop.net/viewtopic.php?t=6299

This can be verified to be correct by first splitting the amount <= loc.value case in two

```
                    } else if (amount < loc.value) {
                        loc.value -= amount;
                        amount = 0;
                    } else if (amount == loc.value) {
                        loc.value -= amount;
                        amount = 0;
                        items.RemoveItem(loc);
                    } else {
                        amount -= loc.value;
                        items.RemoveItem(loc);
                    }
```
then with some refactos to verify than the "equal" case can be merged into the default one

Assets/Scripts/Game/Entities/PlayerEntity.cs

@@ -1331,7 +1331,7 @@ public int DeductGoldAmount(int amount)
                     DaggerfallUnityItem loc = items.GetItem(ItemGroups.MiscItems, (int)MiscItems.Letter_of_credit);
                     if (loc == null) {
                         break;
-                    } else if (amount <= loc.value) {
+                    } else if (amount < loc.value) {
                         loc.value -= amount;
                         amount = 0;
                     } else {