Fix dismissal on the Old Architecture

Summary:
The recent change to make onDismiss work on Fabric broke the Modal on Paper (see [this comment](https://www.internalfb.com/diff/D52959996?dst_version_fbid=236415652884499&transaction_fbid=896066412296150)).

This change will fix that behavior.

The problem was that we were resetting the `isRendered` state only when the Modal receives the event from the Event emitter AND if it has the `onDismiss` callback set.
However, we should hide the component in any case if the ids match, and invoke the onDismiss if it is set.

## Changelog
[iOS][Fixed] - Make sure that Modal is dismissed correctly in Paper

Reviewed By: janeli-100005636499545

Differential Revision: D53686165

fbshipit-source-id: a1de0b29dca7c099e9fa0282ec80cae9a8fd6bc3

packages/react-native/Libraries/Modal/Modal.js

@@ -207,19 +207,18 @@ class Modal extends React.Component<Props, State> {
       this._eventSubscription = ModalEventEmitter.addListener(
         'modalDismissed',
         event => {
-          if (event.modalID === this._identifier && this.props.onDismiss) {
-            this.setState({isRendered: false}, () => {
-              if (this.props.onDismiss) {
-                this.props.onDismiss();
-              }
-            });
-          }
+          this.setState({isRendered: false}, () => {
+            if (event.modalID === this._identifier && this.props.onDismiss) {
+              this.props.onDismiss();
+            }
+          });
         },
       );
     }
   }
 
   componentWillUnmount() {
+    this.setState({isRendered: false});
     if (this._eventSubscription) {
       this._eventSubscription.remove();
     }

packages/react-native/React/Views/RCTModalHostViewManager.m

@@ -98,8 +98,13 @@ - (void)dismissModalHostView:(RCTModalHostView *)modalHostView
   dispatch_async(dispatch_get_main_queue(), ^{
     if (self->_dismissalBlock) {
       self->_dismissalBlock([modalHostView reactViewController], viewController, animated, completionBlock);
-    } else {
+    } else if (viewController.presentingViewController) {
       [viewController.presentingViewController dismissViewControllerAnimated:animated completion:completionBlock];
+    } else {
+      // Make sure to call the completion block in case the presenting view controller is nil
+      // In an internal app we have a use case where a modal presents another view without bein dismissed
+      // This, somehow, invalidate the presenting view controller and the modal remains always visible.
+      completionBlock();
     }
   });
 }