Move displayBlankSnapshotWindow into applicationDidEnterBackground. (duckduckgo#773)

This will prevent the blank window from appearing in cases where something has caused the app to resign active, but it is still in the foreground.

One example is system-level Apple ID authentication on icloud.com.

Author: samsymons

DuckDuckGo/AppDelegate.swift

@@ -175,10 +175,6 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
         showKeyboardIfSettingOn = false
     }
 
-    func applicationWillResignActive(_ application: UIApplication) {
-        displayBlankSnapshotWindow()
-    }
-    
     private func onApplicationLaunch(_ application: UIApplication) {
         beginAuthentication()
         initialiseBackgroundFetch(application)
@@ -196,6 +192,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
     }
 
     func applicationDidEnterBackground(_ application: UIApplication) {
+        displayBlankSnapshotWindow()
         autoClear?.applicationDidEnterBackground()
     }