added error message when deck can't be saved

cockatrice/src/window_deckeditor.cpp

@@ -308,7 +308,8 @@ bool WndDeckEditor::actSaveDeck()
 	else if (deckModel->getDeckList()->saveToFile(lastFileName, lastFileFormat)) {
 		setWindowModified(false);
 		return true;
-	} else
+	}
+	QMessageBox::critical(this, tr("Error"), tr("The deck could not be saved.\nPlease check that the directory is writable and try again."));
 	return false;
 }
 
@@ -332,6 +333,7 @@ bool WndDeckEditor::actSaveDeckAs()
 		setWindowModified(false);
 		return true;
 	}
+	QMessageBox::critical(this, tr("Error"), tr("The deck could not be saved.\nPlease check that the directory is writable and try again."));
 	return false;
 }