[GTFS Fares v2] Update forbidden for network_id in routes.txt if networks.txt exists too (google#581)

Update forbidden for routes.txt's network_id if networks.txt exists too

Author: skalexch

gtfs/spec/en/reference.md

@@ -245,7 +245,7 @@ Primary key (`route_id`)
 |  `route_sort_order` | Non-negative integer | Optional | Orders the routes in a way which is ideal for presentation to customers. Routes with smaller `route_sort_order` values should be displayed first. |
 |  `continuous_pickup` | Enum | **Conditionally Forbidden** | Indicates that the rider can board the transit vehicle at any point along the vehicle’s travel path as described by [shapes.txt](#shapestxt), on every trip of the route. Valid options are: <br><br>`0` - Continuous stopping pickup. <br>`1` or empty - No continuous stopping pickup. <br>`2` - Must phone agency to arrange continuous stopping pickup. <br>`3` - Must coordinate with driver to arrange continuous stopping pickup.  <br><br>Values for `routes.continuous_pickup` may be overridden by defining values in `stop_times.continuous_pickup` for specific `stop_time`s along the route. <br><br>**Conditionally Forbidden**:<br>- Any value other than `1` or empty is **Forbidden** if `stop_times.start_pickup_drop_off_window` or `stop_times.end_pickup_drop_off_window` are defined for any trip of this route.<br> - Optional otherwise. |
 |  `continuous_drop_off` | Enum | **Conditionally Forbidden** | Indicates that the rider can alight from the transit vehicle at any point along the vehicle’s travel path as described by [shapes.txt](#shapestxt), on every trip of the route. Valid options are: <br><br>`0` - Continuous stopping drop off. <br>`1` or empty - No continuous stopping drop off. <br>`2` - Must phone agency to arrange continuous stopping drop off. <br>`3` - Must coordinate with driver to arrange continuous stopping drop off. <br><br>Values for `routes.continuous_drop_off` may be overridden by defining values in `stop_times.continuous_drop_off` for specific `stop_time`s along the route. <br><br>**Conditionally Forbidden**:<br>- Any value other than `1` or empty is **Forbidden** if `stop_times.start_pickup_drop_off_window` or `stop_times.end_pickup_drop_off_window` are defined for any trip of this route.<br> - Optional otherwise. |
-| `network_id` | ID | **Conditionally Forbidden** | Identifies a group of routes. Multiple rows in [routes.txt](#routestxt) may have the same `network_id`.<br><br>Conditionally Forbidden:<br>- **Forbidden** if the [route_networks.txt](#route_networkstxt) file exists.<br>- Optional otherwise. 
+| `network_id` | ID | **Conditionally Forbidden** | Identifies a group of routes. Multiple rows in [routes.txt](#routestxt) may have the same `network_id`.<br><br>Conditionally Forbidden:<br>- **Forbidden** if the [route_networks.txt](#route_networkstxt) or [networks.txt](#networkstxt) file exists.<br>- Optional otherwise. 
 |  `cemv_support` | Enum | Optional | Indicates if riders can access a transit service (i.e., trip) associated with this route by using a contactless EMV (Europay, Mastercard, and Visa) card or mobile device as fare media at a fare validator (such as in pay-as-you-go or open-loop systems). This field does not indicate that cEMV can be used to purchase other fare products or to add value to another fare media. <br><br> Support for cEMVs should only be indicated if all services under this route are accessible with the use of cEMV cards or mobile devices as fare media. <br><br> Valid options are: <br><br>`0` or empty - No cEMV information for trips associated with this route. <br>`1` - Riders may use cEMVs as fare media for trips associated with this route. <br>`2` - cEMVs are not supported as fare media for trips associated with this route. <br><br> If both `agency.cemv_support` and `routes.cemv_support` are provided for the same service, the value in `routes.cemv_support` shall take precedence. <br><br> This field is independent of all other fare-related files and may be used separately.  If there is conflicting information between this field and any fare-related file (such as `fare_media.txt`, `fare_products.txt`, or `fare_leg_rules.txt`), the information in those files shall take precedence over `agency.cemv_support`.
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