Don't crash during Auto Recovery

Steps:

1)	New project
2)	Generate chirp
3)	New Project
4)	Generate chirp
5)	Kill Audacity
6)	Restart Audacity
7)	Unselect the 2nd item
8)	Click "Discard Selected"
9)	Click "Yes" to confirm
10)     Click "Recovery Selected"

Crash...

src/AutoRecoveryDialog.cpp

@@ -275,6 +275,8 @@ void AutoRecoveryDialog::OnDiscardSelected(wxCommandEvent &WXUNUSED(evt))
       }
       if (!mFileList->IsItemChecked(item))
       {
+         // Keep in list
+         files.push_back(mFiles[item]);
          continue;
       }
       FilePath fileName = mFiles[item];