Don't show screen block until app is ready.

Signal/src/ViewControllers/LoadingViewController.swift

@@ -50,7 +50,7 @@ public class LoadingViewController: UIViewController {
 
     var isShowingTopLabel = false
     var isShowingBottomLabel = false
-    override public func viewDidAppear(_ animated: Bool) {
+    override public func viewWillAppear(_ animated: Bool) {
         super.viewWillAppear(animated)
 
         // We only show the "loading" UI if it's a slow launch. Otherwise this ViewController

Signal/src/util/OWSScreenLockUI.m

@@ -130,8 +130,9 @@ NS_ASSUME_NONNULL_BEGIN
 
     [self observeNotifications];
 
-    // Default to screen protection until we know otherwise.
-    [self updateScreenBlockingWindow:ScreenLockUIStateScreenProtection animated:NO];
+    // Hide the screen blocking window until "app is ready" to
+    // avoid blocking the loading view.
+    [self updateScreenBlockingWindow:ScreenLockUIStateNone animated:NO];
 
     // Initialize the screen lock state.
     //

SignalMessaging/ViewControllers/ScreenLockViewController.m

@@ -76,6 +76,8 @@ NSString *NSStringForScreenLockUIState(ScreenLockUIState value)
 
     self.screenBlockingImageView = imageView;
     self.screenBlockingButton = button;
+
+    [self updateUIWithState:ScreenLockUIStateScreenProtection isLogoAtTop:NO animated:NO];
 }
 
 // The "screen blocking" window has three possible states:
@@ -89,6 +91,10 @@ NSString *NSStringForScreenLockUIState(ScreenLockUIState value)
 {
     OWSAssertIsOnMainThread();
 
+    if (!self.screenBlockingImageView) {
+        return;
+    }
+
     BOOL shouldShowBlockWindow = uiState != ScreenLockUIStateNone;
     BOOL shouldHaveScreenLock = uiState == ScreenLockUIStateScreenLock;