alsactl: don't free a card pointing NULL

alsactl distributed as part of Fedora 40 got a SEGV:

    # journalctl
    ...
    May 17 00:55:58 dev64.localdomain kernel: alsactl[1923]: segfault at 28 ip 00005600705b3373 sp 00007ffd9712bef0 error 4 in alsactl[5600705af000+13000] likely on CPU 5 (core 8, socket 0)
    ...

As the following output of the debug session, card_free() tried a card
pointing NULL:

    $ sudo coredumpctl debug alsactl
	       PID: 1923 (alsactl)
	       UID: 0 (root)
	       GID: 0 (root)
	    Signal: 11 (SEGV)
	 Timestamp: Fri 2024-05-17 00:55:58 JST (3h 34min ago)
      Command Line: /usr/sbin/alsactl -s -n 19 -c -E ALSA_CONFIG_PATH=/etc/alsa/alsactl.conf --initfile=/lib/alsa/init/00main rdaemon
	Executable: /usr/sbin/alsactl
     Control Group: /system.slice/alsa-state.service
	      Unit: alsa-state.service
	     Slice: system.slice
	   Boot ID: 241b5a2ef86f4940bb3d340583c80d88
	Machine ID: 437365709a8c488c9481ee4b6651c2ec
	  Hostname: dev64.localdomain
	   Storage: /var/lib/systemd/coredump/core.alsactl.0.241b5a2ef86f4940bb3d340583c80d88.1923.1715874958000000.zst (present)
      Size on Disk: 81.7K
	   Package: alsa-utils/1.2.11-1.fc40
	  build-id: 3b6fec58b3566d666d6e9fd48e8fcf04f03f0152
	   Message: Process 1923 (alsactl) of user 0 dumped core.

		    Module libasound.so.2 from rpm alsa-lib-1.2.11-2.fc40.x86_64
		    Module alsactl from rpm alsa-utils-1.2.11-1.fc40.x86_64
		    Stack trace of thread 1923:
		    #0  0x00005600705b3373 card_free (alsactl + 0xa373)
		    #1  0x00005600705c0e54 state_daemon (alsactl + 0x17e54)
		    #2  0x00005600705b2339 main (alsactl + 0x9339)
		    #3  0x00007f4c0b9b7088 __libc_start_call_main (libc.so.6 + 0x2a088)
		    #4  0x00007f4c0b9b714b __libc_start_main_impl (libc.so.6 + 0x2a14b)
		    #5  0x00005600705b2df5 _start (alsactl + 0x9df5)
		    ELF object binary architecture: AMD x86-64

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    Reading symbols from /usr/sbin/alsactl...
    Reading symbols from /usr/lib/debug/usr/sbin/alsactl-1.2.11-1.fc40.x86_64.debug...
    [New LWP 1923]
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib64/libthread_db.so.1".
    Core was generated by `/usr/sbin/alsactl -s -n 19 -c -E ALSA_CONFIG_PATH=/etc/alsa/alsactl.conf --init'.
    Program terminated with signal SIGSEGV, Segmentation fault.
    #0  free_list (list=0x20) at /usr/src/debug/alsa-utils-1.2.11-1.fc40.x86_64/alsactl/daemon.c:73
    73		for (i = 0; i < list->size; i++)
    (gdb) where
    #0  free_list (list=0x20) at /usr/src/debug/alsa-utils-1.2.11-1.fc40.x86_64/alsactl/daemon.c:73
    #1  card_free (card=card@entry=0x5600707455f0) at /usr/src/debug/alsa-utils-1.2.11-1.fc40.x86_64/alsactl/daemon.c:82
    #2  0x00005600705c0e54 in state_daemon (file=file@entry=0x5600705c31a1 "/var/lib/alsa/asound.state", cardname=cardname@entry=0x0, period=period@entry=300,
	pidfile=pidfile@entry=0x5600705c3170 "/var/run/alsactl.pid") at /usr/src/debug/alsa-utils-1.2.11-1.fc40.x86_64/alsactl/daemon.c:455
    #3  0x00005600705b2339 in main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/alsa-utils-1.2.11-1.fc40.x86_64/alsactl/alsactl.c:459
    (gdb) list
    68
    69	static void free_list(struct id_list *list)
    70	{
    71		int i;
    72
    73		for (i = 0; i < list->size; i++)
    74			free(list->list[i]);
    75		free(list->list);
    76	}
    77
    (gdb) up
    #1  card_free (card=card@entry=0x5600707455f0) at /usr/src/debug/alsa-utils-1.2.11-1.fc40.x86_64/alsactl/daemon.c:82
    82		free_list(&c->blacklist);
    (gdb) p c
    $1 = (struct card *) 0x0
    (gdb)

Closes: #267
Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

alsactl/daemon.c

@@ -79,6 +79,8 @@ static void card_free(struct card **card)
 {
 	struct card *c = *card;
 
+	if (c == NULL)
+		return;
 	free_list(&c->blacklist);
 	free_list(&c->whitelist);
 	if (c->handle)