fix: don't crash when command_ctl table not init

apps/emqx_ctl/src/emqx_ctl.erl

@@ -128,16 +128,21 @@ run_command(Cmd, Args) when is_atom(Cmd) ->
                     }),
                     {error, Reason}
             end;
-        [] ->
+        Error ->
             help(),
-            {error, cmd_not_found}
+            Error
     end.
 
 -spec lookup_command(cmd()) -> [{module(), atom()}].
 lookup_command(Cmd) when is_atom(Cmd) ->
+    case is_init() of
+        true ->
             case ets:match(?CMD_TAB, {{'_', Cmd}, '$1', '_'}) of
                 [El] -> El;
-        [] -> []
+                [] -> {error, cmd_not_found}
+            end;
+        false ->
+            {error, cmd_is_initializing}
     end.
 
 -spec get_commands() -> list({cmd(), module(), atom()}).
@@ -145,6 +150,8 @@ get_commands() ->
     [{Cmd, M, F} || {{_Seq, Cmd}, {M, F}, _Opts} <- ets:tab2list(?CMD_TAB)].
 
 help() ->
+    case is_init() of
+        true ->
             case ets:tab2list(?CMD_TAB) of
                 [] ->
                     print("No commands available.~n");
@@ -157,6 +164,9 @@ help() ->
                         end,
                         Cmds
                     )
+            end;
+        false ->
+            print("Command table is initializing.~n")
     end.
 
 -spec print(io:format()) -> ok.
@@ -279,3 +289,6 @@ safe_to_existing_atom(Str) ->
         _:badarg ->
             undefined
     end.
+
+is_init() ->
+    ets:info(?CMD_TAB) =/= undefined.