Fix log for writing to nonexistent socket

[michaelortmann]

Found by: michaelortmann
Patch by: michaelortmann
Fixes:

One-line summary:
Fix log for writing to nonexistent socket

Additional description (if needed):
Bug was introduced by #1467.

Test cases demonstrating functionality (if applicable):

./configure --disable-tls
...
make
...
gcc -std=gnu99 -g -O2 -pipe -Wall -I.. -I..  -DHAVE_CONFIG_H -I/usr/include  -c net.c
net.c: In function ‘tputs’:
net.c:1394:33: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
 1394 |     putlog(LOG_MISC, "*", "!-> '%s'", s2);
      |                                 ^~