Handle all wxCalendarHitTestResult elements in a switch

This ensures that the compiler will warn us if a new wxCAL_HITTEST_XXX is
added but forgotten to be handled here.

src/generic/calctrlg.cpp

@@ -1339,8 +1339,12 @@ void wxGenericCalendarCtrl::OnDClick(wxMouseEvent& event)
             SetDateAndNotify(date);
             break;
 
-        default:
+        case wxCAL_HITTEST_WEEK:
+        case wxCAL_HITTEST_HEADER:
+        case wxCAL_HITTEST_SURROUNDING_WEEK:
+        case wxCAL_HITTEST_NOWHERE:
             event.Skip();
+            break;
     }
 }