missingmotd: Include nick in IRC numeric command

Since the nick argument is missing, "MOTD File is missing" is taking the
nicks place and could lead to client confusion that the 422 command is
sent to "MOTD File is missing".

modules/missingmotd.cpp

@@ -15,13 +15,14 @@
  */
 
 #include <znc/Modules.h>
+#include <znc/Client.h>
 
 class CMissingMotd : public CModule {
   public:
     MODCONSTRUCTOR(CMissingMotd) {}
 
     void OnClientLogin() override {
-        PutUser(":irc.znc.in 422 :MOTD File is missing");
+        PutUser(":irc.znc.in 422 " + GetClient()->GetNick() + " :MOTD File is missing");
     }
 };