Configuration GUI: Make radio buttons properly tabbable

src/gui/sdl_gui.cpp

@@ -789,6 +789,24 @@ class ShowOptions : public GUI::MessageBox2 {
             close->move(155,scroll_h+90);
             resize(310, scroll_h+156);
             move(parent->getWidth()>this->getWidth()?(parent->getWidth()-this->getWidth())/2:0,parent->getHeight()>this->getHeight()?(parent->getHeight()-this->getHeight())/2:0);
+
+            /* first child is first tabbable */
+            if (pv.size() > 0) {
+                Window *w = opt[0];
+                if (w) w->first_tabbable = true;
+            }
+
+            /* last child is first tabbable */
+            if (pv.size() > 0) {
+                Window *w = opt[pv.size()-1];
+                if (w) w->last_tabbable = true;
+            }
+
+            /* the FIRST field needs to come first when tabbed to */
+            if (pv.size() > 0) {
+                Window *w = opt[0];
+                if (w) w->raise();
+            }
     }
 
     void actionExecuted(GUI::ActionEventSource *b, const GUI::String &arg) override {