avoid gcc warning about switch

git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@4771 212acab6-be3b-0410-9dea-997c60f758d6

Source/manifest.cpp

@@ -25,6 +25,8 @@ string generate(comctl comctl_selection, exec_level exec_level_selection)
 
     switch (exec_level_selection)
     {
+    case exec_level_none:
+      break;
     case exec_level_user:
       level = "asInvoker";
       break;