[NavigationDrawer] Fix broken header when content expands (material-c…

…omponents#8514)

In material-components#8503 this line was removed but after further testing when the contentViewController expands it's preferredContentSize this causes a regression in the header behavior. With this line added back into the check this behavior is fixed.

components/NavigationDrawer/src/private/MDCBottomDrawerContainerViewController.m

@@ -661,7 +661,8 @@ - (void)updateViewWithContentOffset:(CGPoint)contentOffset {
                                                        transitionRatio:transitionPercentage];
 
   [self updateDrawerState:transitionPercentage];
-  self.currentlyFullscreen = self.contentReachesFullscreen && contentOffset.y > 0;
+  self.currentlyFullscreen =
+      self.contentReachesFullscreen && headerTransitionToTop >= 1 && contentOffset.y > 0;
   CGFloat fullscreenHeaderHeight =
       self.contentReachesFullscreen ? self.topHeaderHeight : [self contentHeaderHeight];