fix a crash when scanning false QR code to link a device

Session/Meta/Translations/en.lproj/Localizable.strings

@@ -564,4 +564,5 @@
 "accessibility_library_button" = "Photo library";
 "accessibility_camera_button" = "Camera";
 "accessibility_main_button_collapse" = "Collapse attachment options";
+"invalid_recovery_phrase" = "Invalid Recovery Phrase";
 

Session/Onboarding/LinkDeviceVC.swift

@@ -122,6 +122,14 @@ final class LinkDeviceVC : BaseVC, UIPageViewControllerDataSource, UIPageViewCon
     }
     
     func continueWithSeed(_ seed: Data) {
+        if (seed.count != 16) {
+            let alert = UIAlertController(title: NSLocalizedString("invalid_recovery_phrase", comment: ""), message: NSLocalizedString("Please check the Recovery Phrase and try again.", comment: ""), preferredStyle: .alert)
+            alert.addAction(UIAlertAction(title: NSLocalizedString("OK", comment: ""), style: .default, handler: { _ in
+                self.scanQRCodeWrapperVC.startCapture()
+            }))
+            presentAlert(alert)
+            return
+        }
         let (ed25519KeyPair, x25519KeyPair) = KeyPairUtilities.generate(from: seed)
         Onboarding.Flow.link.preregister(with: seed, ed25519KeyPair: ed25519KeyPair, x25519KeyPair: x25519KeyPair)
         TSAccountManager.sharedInstance().didRegister()

Session/Shared/ScanQRCodeWrapperVC.swift

@@ -71,4 +71,10 @@ final class ScanQRCodeWrapperVC : BaseVC {
     @objc private func close() {
         presentingViewController?.dismiss(animated: true, completion: nil)
     }
+    
+    public func startCapture() {
+        DispatchQueue.main.async { [weak self] in
+            self?.scanQRCodeVC.startCapture()
+        }
+    }
 }