safe-fail if old file can't be deleted

Pilz.Updating.Client/Utils.cs

@@ -25,6 +25,7 @@ public static class Utils
         var triesLeft = 1;
         var srcFileName = sourceFile.FullName;
         var destFileName = destinationFile.FullName;
+        string? oldFile = null;
 
         while (triesLeft > 0)
         {
@@ -38,9 +39,8 @@ public static class Utils
             {
                 if (triesLeft == 0 && File.Exists(destFileName))
                 {
-                    var oldFile = destFileName + ".old";
+                    oldFile = destFileName + ".old";
                     File.Move(destFileName, oldFile, true);
-                    File.Delete(oldFile);
                     triesLeft++;
                 }
             }
@@ -48,5 +48,16 @@ public static class Utils
             {
             }
         }
+
+        if (oldFile != null)
+        {
+            try
+            {
+                File.Delete(oldFile);
+            }
+            catch (Exception)
+            {
+            }
+        }
     }
 }