menu: support :emenu invoked by cmenu map.

src/nvim/menu.c

@@ -1262,6 +1262,9 @@ void ex_emenu(exarg_T *eap)
   if (((State & INSERT) || restart_edit) && !current_SID) {
     mode = (char_u *)"Insert";
     idx = MENU_INDEX_INSERT;
+  } else if (State & CMDLINE) {
+      mode = (char_u *)"Command";
+      idx = MENU_INDEX_CMDLINE;
   } else if (get_real_state() & VISUAL) {
     /* Detect real visual mode -- if we are really in visual mode we
      * don't need to do any guesswork to figure out what the selection