batchForm.cs: Added try-catch block to handle file in use exceptions

- Added try-catch block to handle exceptions when importing batch
- Displayed error message and notification form if an exception occurs

FireWallet/BatchForm.cs

@@ -637,6 +637,8 @@ namespace FireWallet
             openFileDialog.Filter = "All Files|*.*";
             openFileDialog.Title = "Open Batch";
             if (openFileDialog.ShowDialog() == DialogResult.OK)
+            {
+                try
                 {
                     StreamReader sr = new StreamReader(openFileDialog.FileName);
                     string line;
@@ -718,6 +720,13 @@ namespace FireWallet
                         }
                     }
                     sr.Dispose();
+                } catch (Exception ex)
+                {
+                    AddLog("Error importing batch: " + ex.Message);
+                    NotifyForm notifyForm = new NotifyForm("Error importing batch\nMake sure the file is in not in use");
+                    notifyForm.ShowDialog();
+                    notifyForm.Dispose();
+                }
             }
         }