fix(cmd_sub): Prevent crash with malformed JID in /sub command

Added null check for jidp in cmd_sub to handle jid_create returning NULL.

Crash occurred when processing malformed JID inputs like @example.com.

Ensures robust handling of invalid JIDs.

Fixes #22

src/command/cmd_funcs.c

@@ -1263,6 +1263,11 @@ cmd_sub(ProfWin* window, const char* const command, gchar** args)
 
     auto_jid Jid* jidp = jid_create(jid);
 
+    if (jidp == NULL) {
+        cons_show("Malformed JID: %s", jid);
+        return TRUE;
+    }
+
     if (strcmp(subcmd, "allow") == 0) {
         presence_subscription(jidp->barejid, PRESENCE_SUBSCRIBED);
         cons_show("Accepted subscription for %s", jidp->barejid);