fix: use header height from style if specified

src/views/Stack/Stack.tsx

@@ -114,14 +114,20 @@ const ANIMATED_ONE = new Animated.Value(1);
 const getFloatingHeaderHeights = (
   routes: NavigationRoute[],
   insets: EdgeInsets | null,
+  descriptors: SceneDescriptorMap,
   layout: Layout,
   previous: { [key: string]: number }
 ) => {
   const defaultHeaderHeight = getDefaultHeaderHeight(layout, insets);
 
   return routes.reduce(
     (acc, curr) => {
-      acc[curr.key] = previous[curr.key] || defaultHeaderHeight;
+      const { options = {} } = descriptors[curr.key] || {};
+      const { height = previous[curr.key] } = StyleSheet.flatten(
+        options.headerStyle || {}
+      );
+
+      acc[curr.key] = typeof height === 'number' ? height : defaultHeaderHeight;
 
       return acc;
     },
@@ -202,6 +208,7 @@ export default class Stack extends React.Component<Props, State> {
       floatingHeaderHeights: getFloatingHeaderHeights(
         props.routes,
         props.insets,
+        state.descriptors,
         state.layout,
         state.floatingHeaderHeights
       ),
@@ -234,15 +241,16 @@ export default class Stack extends React.Component<Props, State> {
 
     const layout = { width, height };
 
-    this.setState({
+    this.setState(state => ({
       layout,
       floatingHeaderHeights: getFloatingHeaderHeights(
         this.props.routes,
         this.props.insets,
+        state.descriptors,
         layout,
         {}
       ),
-    });
+    }));
   };
 
   private handleFloatingHeaderLayout = ({