A couple of checks for corner cases in RCTGetDimensions and RCTExportedDimensions

Summary: We need this checks to make the results of those function more reliable.

Reviewed By: sammy-SC

Differential Revision: D24038911

fbshipit-source-id: 3b54fe3056c9508cde84ea157beebea57e7e49b6

Author: shergin

React/CoreModules/RCTDeviceInfo.mm

@@ -93,7 +93,8 @@ static BOOL RCTIsIPhoneX()
 static NSDictionary *RCTExportedDimensions(RCTBridge *bridge)
 {
   RCTAssertMainQueue();
-  RCTDimensions dimensions = RCTGetDimensions(bridge.accessibilityManager.multiplier);
+  RCTAssert(bridge, @"Bridge must not be `nil`.");
+  RCTDimensions dimensions = RCTGetDimensions(bridge.accessibilityManager.multiplier ?: 1.0);
   __typeof(dimensions.window) window = dimensions.window;
   NSDictionary<NSString *, NSNumber *> *dimsWindow = @{
     @"width" : @(window.width),

React/UIUtils/RCTUIUtils.m

@@ -16,7 +16,8 @@ RCTDimensions RCTGetDimensions(CGFloat fontScale)
 
   UIView *mainWindow;
   mainWindow = RCTKeyWindow();
-  CGSize windowSize = mainWindow.bounds.size;
+  // We fallback to screen size if a key window is not found.
+  CGSize windowSize = mainWindow ? mainWindow.bounds.size : screenSize;
 
   RCTDimensions result;
   typeof(result.screen) dimsScreen = {