use auth_name as placeholder during contact name editing

DcCore/DcCore/DC/Wrapper.swift

@@ -1086,6 +1086,13 @@ public class DcContact {
         return swiftString
     }
 
+    public var authName: String {
+        guard let cString = dc_contact_get_auth_name(contactPointer) else { return "" }
+        let swiftString = String(cString: cString)
+        dc_str_unref(cString)
+        return swiftString
+    }
+
     public var email: String {
         guard let cString = dc_contact_get_addr(contactPointer) else { return "" }
         let swiftString = String(cString: cString)

deltachat-ios/Controller/EditContactController.swift

@@ -11,8 +11,11 @@ class EditContactController: NewContactController {
         title = String.localized("edit_contact")
 
         let contact = DcContact(id: contactIdForUpdate)
+
         nameCell.textField.text = contact.editedName
-        nameCell.placeholder = contact.displayName
+        if !contact.authName.isEmpty { // else show string "Name" as set by super.init()
+            nameCell.placeholder = contact.authName
+        }
         emailCell.textField.text = contact.email
         emailCell.textField.isEnabled = false
         emailCell.contentView.alpha = 0.3