prefer 'guard let self ...' over 'self?' if self is used multiple times. this avoids thinking over what would happen if self disappears between the calls ... don't make me think :)

deltachat-ios/Controller/NewGroupController.swift

@@ -368,8 +368,9 @@ class NewGroupController: UITableViewController, MediaPickerDelegate {
         let newGroupController = NewGroupAddMembersViewController(preselected: preselectedMembers,
                                                                   isVerified: isVerified)
         newGroupController.onMembersSelected = { [weak self] (memberIds: Set<Int>) -> Void in
-            self?.updateGroupContactIdsOnListSelection(memberIds)
-            self?.navigationController?.popViewController(animated: true)
+            guard let self = self else { return }
+            self.updateGroupContactIdsOnListSelection(memberIds)
+            self.navigationController?.popViewController(animated: true)
         }
         navigationController?.pushViewController(newGroupController, animated: true)
     }

deltachat-ios/Controller/WelcomeViewController.swift

@@ -26,10 +26,11 @@ class WelcomeViewController: UIViewController, ProgressAlertHandler {
             self.navigationController?.pushViewController(accountSetupController, animated: true)
         }
         view.onScanQRCode  = { [weak self] in
+            guard let self = self else { return }
             let qrReader = QrCodeReaderController()
             qrReader.delegate = self
-            self?.qrCodeReader = qrReader
-            self?.navigationController?.pushViewController(qrReader, animated: true)
+            self.qrCodeReader = qrReader
+            self.navigationController?.pushViewController(qrReader, animated: true)
         }
         view.translatesAutoresizingMaskIntoConstraints = false
         return view
@@ -149,8 +150,9 @@ extension WelcomeViewController: QrCodeReaderDelegate {
             title: String.localized("ok"),
             style: .default,
             handler: { [weak self] _ in
-                self?.dismissQRReader()
-                self?.createAccountFromQRCode(qrCode: qrCode)
+                guard let self = self else { return }
+                self.dismissQRReader()
+                self.createAccountFromQRCode(qrCode: qrCode)
             }
         )