Fix a missing free in random-test-client

Thanks again to Stefan Finzel.
It would be nice to run Valgrind more often...

tests/random-test-client.c

@@ -244,6 +244,7 @@ int main(void)
     free(tab_rp_bits);
     free(tab_rq_registers);
     free(tab_rp_registers);
+    free(tab_rw_rp_registers);
 
     /* Close the connection */
     modbus_close(ctx);