nmcli: always clean up readline on exit

A signal handler is not the only place where we need to clean up after
an in-progress readline() on exit; we may do so when erroring out as
well:

Before (not also the missing line break, which is part of the cleanup):

  $ (sleep 10; nmcli c del 'Red Hat Wi-Fi')
  $ nmcli --ask d wifi connect 'Red Hat Wi-Fi'
  Passwords or encryption keys are required to access the wireless network 'Red Hat Wi-Fi'.
  Password (802-11-wireless-security.psk): Error: Connection activation failed: The device's active connection disappeared.
  $ [terminal messed up, no echo]

After:

  $ (sleep 10; nmcli c del 'Red Hat Wi-Fi')
  $ nmcli --ask d wifi connect 'Red Hat Wi-Fi'
  Passwords or encryption keys are required to access the wireless network 'Red Hat Wi-Fi'.
  Password (802-11-wireless-security.psk):
  Error: Connection activation failed: The device's active connection disappeared.
  $ hello [terminal echo fine, wheee]

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1959

src/nmcli/common.c

@@ -824,7 +824,7 @@ static char    *rl_string;
 /**
  * nmc_cleanup_readline:
  *
- * Cleanup readline when nmcli is terminated with a signal.
+ * Cleanup readline when nmcli is terminated.
  * It makes sure the terminal is not garbled.
  */
 void

src/nmcli/nmcli.c

@@ -1044,6 +1044,8 @@ main(int argc, char *argv[])
     if (process_command_line(&nm_cli, argc, argv))
         g_main_loop_run(loop);
 
+    nmc_cleanup_readline();
+
     if (nm_cli.complete) {
         /* Remove error statuses from command completion runs. */
         if (nm_cli.return_value < NMC_RESULT_COMPLETE_FILE)