fix: don't fire onOpen when screen is unmounting (#137)

I can't think of a scenario a screen would unmount when opening.
So it's probably a safe-bet to always call onClose.

Fixes #136

packages/stack/src/views/Stack/Card.tsx

@@ -281,19 +281,11 @@ export default class Card extends React.Component<Props> {
     // during running. However, we need to invoke listener onClose
     // manually in this case
     if (this.isRunningAnimation || this.noAnimationStartedSoFar) {
-      if (this.isVisibleValue) {
-        this.props.onOpen(false);
-      } else {
-        this.props.onClose(false);
-      }
+      this.props.onClose(false);
     }
   }
 
   private isVisible = new Value<Binary>(TRUE);
-  private gestureVelocityImpact = new Value<number>(
-    this.props.gestureVelocityImpact
-  );
-  private isVisibleValue: Binary = TRUE;
   private nextIsVisible = new Value<Binary | -1>(UNSET);
 
   private isClosing = new Value<Binary>(FALSE);
@@ -313,7 +305,11 @@ export default class Card extends React.Component<Props> {
     height: new Value(this.props.layout.height),
   };
 
-  openingSpecConfig =
+  private gestureVelocityImpact = new Value<number>(
+    this.props.gestureVelocityImpact
+  );
+
+  private openingSpecConfig =
     this.props.transitionSpec.open.animation === 'timing'
       ? transformTimingConfigToAnimatedValues(
           this.props.transitionSpec.open.config
@@ -322,7 +318,7 @@ export default class Card extends React.Component<Props> {
           this.props.transitionSpec.open.config
         );
 
-  closingSpecConfig =
+  private closingSpecConfig =
     this.props.transitionSpec.close.animation === 'timing'
       ? transformTimingConfigToAnimatedValues(
           this.props.transitionSpec.close.config
@@ -533,19 +529,9 @@ export default class Card extends React.Component<Props> {
     ),
   ];
 
-  private changeVisiblityExec = onChange(
-    this.isVisible,
-    call([this.isVisible], ([isVisible]) => (this.isVisibleValue = isVisible))
-  );
-
   private execNoGesture = block([
     ...this.exec,
     this.runTransition(this.isVisible),
-    onChange(
-      this.isVisible,
-      call([this.isVisible], ([isVisible]) => (this.isVisibleValue = isVisible))
-    ),
-    this.changeVisiblityExec,
   ]);
 
   private execWithGesture = block([
@@ -654,7 +640,6 @@ export default class Card extends React.Component<Props> {
         ),
       ]
     ),
-    this.changeVisiblityExec,
   ]);
 
   private handleGestureEventHorizontal = Animated.event([