only invoke smkx when attached to a tty

src/lib/termdesc.c

@@ -786,6 +786,7 @@ int interrogate_terminfo(tinfo* ti, const char* termtype, FILE* out, unsigned ut
     logpanic("Required terminfo capability 'cup' not defined\n");
     goto err;
   }
+  if(ti->ttyfd >= 0){
     // if the keypad neen't be explicitly enabled, smkx is not present
     const char* smkx = get_escape(ti, ESCAPE_SMKX);
     if(smkx){
@@ -794,6 +795,7 @@ int interrogate_terminfo(tinfo* ti, const char* termtype, FILE* out, unsigned ut
         goto err;
       }
     }
+  }
   if(ti->caps.colors > 1){
     const char* initc = get_escape(ti, ESCAPE_INITC);
     if(initc){