Fix #25: Program throws exception when clicking on the 'stylesheet' list if there are no stylesheets.

git-svn-id: svn://svn.code.sf.net/p/magicseteditor/code/trunk@1450 0fc631ac-6414-0410-93d0-97cfa31319b6

src/gui/new_window.cpp

@@ -90,6 +90,7 @@ void NewSetWindow::OnOK(wxCommandEvent&) {
 
 void NewSetWindow::done() {
 	try {
+		if (!stylesheet_list->hasSelection()) return;
 		StyleSheetP stylesheet = stylesheet_list->getSelection<StyleSheet>();
 		set = intrusive(new Set(stylesheet));
 		set->validate();