cfg: fix combo boxes (#429)

## Link to GitHub Issue, if one exists
n/a

## Description of change
Combo boxes for options were not highlighting the currently selected
item. Also, when there were no description provided for an option, it
was still showing the empty `()` in the selected value.

## Testing

src/spice2x/overlay/windows/config.cpp

@@ -2828,19 +2828,23 @@ namespace overlay::windows {
                         std::string current_item = option.value_text();
                         for (auto &element : definition.elements) {
                             if (element.first == current_item) {
+                                if (!element.second.empty()) {
                                     current_item += fmt::format(" ({})", element.second);
                                 }
+                                break;
+                            }
                         }
                         if (current_item.empty()) {
                             current_item = "Default";
                         }
                         if (ImGui::BeginCombo("##combo", current_item.c_str(), 0)) {
                             for (auto &element : definition.elements) {
-                                bool selected = current_item == element.first;
                                 std::string label = element.first;
                                 if (!element.second.empty()) {
                                     label += fmt::format(" ({})", element.second);
                                 }
+                                
+                                bool selected = current_item == label;
                                 if (ImGui::Selectable(label.c_str(), selected)) {
                                     this->options_dirty = true;
                                     option.value = element.first;