content-pack id validation + refactor

src/frontend/gui/gui_util.cpp

@@ -37,6 +37,10 @@ void guiutil::alert(GUI* gui, const std::wstring& text, gui::runnable on_hidden)
         size_t offset = 0;
         int extra;
         while ((extra = text.length() - offset) > 0) {
+            size_t endline = text.find(L'\n', offset);
+            if (endline != std::string::npos) {
+                extra = std::min(extra, int(endline-offset)+1);
+            }
             extra = std::min(extra, wrap_length);
             std::wstring part = text.substr(offset, extra);
             panel->add(new Label(part));

src/frontend/menu.cpp

@@ -302,6 +302,13 @@ void create_new_world_panel(Engine* engine, PagesControl* menu) {
         try {
             engine->loadAllPacks();
             engine->loadContent();
+        } catch (const contentpack_error& error) {
+            guiutil::alert(engine->getGUI(),
+                        langs::get(L"Content Error", L"menu")+
+                        L":\n"+util::str2wstr_utf8(std::string(error.what())+
+                                "\npack '"+error.getPackId()+"' from "+
+                                error.getFolder().u8string()));
+            return;
         } catch (const std::runtime_error& error) {
             guiutil::alert(engine->getGUI(),
                         langs::get(L"Content Error", L"menu")+