Linux/MacOSX: make the cancel button work on the preferences dialog.

src/Main/Forms/PreferencesDialog.h

@@ -26,7 +26,7 @@ namespace VeraCrypt
 	protected:
 		void OnAssignHotkeyButtonClick (wxCommandEvent& event);
 		void OnBackgroundTaskEnabledCheckBoxClick (wxCommandEvent& event);
-		void OnCancelButtonClick (wxCommandEvent& event) { Close(); }
+		void OnCancelButtonClick (wxCommandEvent& event) { EndModal (wxID_CANCEL); }
 		void OnClose (wxCloseEvent& event);
 		void OnDismountOnPowerSavingCheckBoxClick (wxCommandEvent& event);
 		void OnDismountOnScreenSaverCheckBoxClick (wxCommandEvent& event);