Add fallback for iOS 13 when not using scenes (#6169)

Author: jeremydurham

FirebaseAppDistribution/Sources/FIRAppDistributionUIService.m

@@ -208,8 +208,8 @@ - (void)initializeUIState {
     if (foregroundedScene) {
       self.window = [[UIWindow alloc] initWithWindowScene:foregroundedScene];
     } else {
-      FIRFADErrorLog(@"No foreground scene found. Cannot display new build alert.");
-      return;
+      FIRFADInfoLog(@"No foreground scene found.");
+      self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
     }
   } else {
     self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];