adding wxFALLTHROUGH where until now we had comments, allows for code-analysis support

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76399 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/config.cpp

@@ -494,7 +494,7 @@ wxString wxExpandEnvVars(const wxString& str)
 
           break;
         }
-        //else: fall through
+        wxFALLTHROUGH;
 
       default:
         strResult += str[n];