[ios][pv]check UIScreen to be nil in platform view overlay setState call (#166024)

A follow up to https://github.com/flutter/flutter/pull/165525

This checks against: 

1. flutterView being nil
2. flutterView's screen being nil
3. flutterView's screen's scale being 0

Again, since we can't repro, I am justing guessing here. 

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Internal only (See previous PR linked above)

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engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm

@@ -16,6 +16,7 @@
 #include "flutter/fml/thread.h"
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Test.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsController.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
@@ -4662,6 +4663,14 @@ fml::RefPtr<fml::TaskRunner> GetDefaultTaskRunner() {
   layer->UpdateViewState(nil, SkRect::MakeXYWH(1, 2, 3, 4), 0, 0);
   // Should not update the view state (e.g. overlay_view_wrapper's frame) when FlutterView is nil.
   XCTAssertTrue(CGRectEqualToRect(layer->overlay_view_wrapper.frame, CGRectZero));
+
+  FlutterView* flutterView = [[FlutterView alloc] initWithDelegate:engine
+                                                            opaque:YES
+                                                   enableWideGamut:NO];
+  layer->UpdateViewState(flutterView, SkRect::MakeXYWH(1, 2, 3, 4), 0, 0);
+  // Should not update the view state (e.g. overlay_view_wrapper's frame) when FlutterView's screen
+  // is nil.
+  XCTAssertTrue(CGRectEqualToRect(layer->overlay_view_wrapper.frame, CGRectZero));
 }
 
 - (void)testFlutterPlatformViewControllerSubmitFramePreservingFrameDamage {

engine/src/flutter/shell/platform/darwin/ios/framework/Source/overlay_layer_pool.mm

@@ -23,12 +23,15 @@ void OverlayLayer::UpdateViewState(UIView* flutter_view,
                                    SkRect rect,
                                    int64_t view_id,
                                    int64_t overlay_id) {
-  // There can be a race where UpdateViewState() is called when flutter_view is nil when app is
-  // backgrounded.
-  if (!flutter_view) {
+  FlutterView* flutterView = (FlutterView*)flutter_view;
+  // There can be a race where UpdateViewState() is called when flutter_view or flutter_view's
+  // screen is nil when app is backgrounded.
+  // It's unlikely for scale to be 0, but just to be safe here since it's used in a scaling
+  // calculation division below
+  if (!flutterView || !flutterView.screen || flutterView.screen.scale == 0.0f) {
     return;
   }
-  auto screenScale = ((FlutterView*)flutter_view).screen.scale;
+  CGFloat screenScale = flutterView.screen.scale;
   // Set the size of the overlay view wrapper.
   // This wrapper view masks the overlay view.
   overlay_view_wrapper.frame = CGRectMake(rect.x() / screenScale, rect.y() / screenScale,