Fails to build with GCC 12

[Martin Liška]

I see the following warning/error:

[   74s] printer.c: In function 'digest_md5_print_response':
[   74s] printer.c:336:7: error: the comparison will always evaluate as 'true' 
for the address of 'response' will never be NULL [-Werror=address]
[   74s]   336 |   if (r->response)
[   74s]       |       ^
[   74s] In file included from printer.h:27,
[   74s]                  from printer.c:28:
[   74s] tokens.h:139:8: note: 'response' declared here
[   74s]   139 |   char response[DIGEST_MD5_RESPONSE_LENGTH + 1];
[   74s]       |        ^~~~~~~~
[   74s] cc1: all warnings being treated as errors

Martin