Error handling: alertText() can be nil

Indicating that no alert is to be shown for that error.

Signed-off-by: Roopesh Chander <roop@roopc.net>

WireGuard/WireGuard/ZipArchive/ZipArchive.swift

@@ -8,7 +8,7 @@ enum ZipArchiveError: WireGuardAppError {
     case cantOpenOutputZipFileForWriting
     case badArchive
 
-    func alertText() -> (String, String) {
+    func alertText() -> (String, String)? {
         switch (self) {
         case .cantOpenInputZipFile:
             return ("Unable to read zip archive", "The zip archive could not be read.")

WireGuard/WireGuard/ZipArchive/ZipExporter.swift

@@ -6,7 +6,7 @@ import UIKit
 enum ZipExporterError: WireGuardAppError {
     case noTunnelsToExport
 
-    func alertText() -> (String, String) {
+    func alertText() -> (String, String)? {
         switch (self) {
         case .noTunnelsToExport:
             return ("Nothing to export", "There are no tunnels to export")

WireGuard/WireGuard/ZipArchive/ZipImporter.swift

@@ -6,7 +6,7 @@ import UIKit
 enum ZipImporterError: WireGuardAppError {
     case noTunnelsInZipArchive
 
-    func alertText() -> (String, String) {
+    func alertText() -> (String, String)? {
         switch (self) {
         case .noTunnelsInZipArchive:
             return ("No tunnels in zip archive", "No .conf tunnel files were found inside the zip archive.")