src/log.c: Fix unexpected termination in logprintf (tiny change)

When errno was set to EPIPE before call to logprintf (e.g. during close of
SSL connection that was reset by peer), it will unexpectedly terminate wget.
It should exit only when EPIPE was triggered by logging code.

Regression by 0b5b100fc9

src/log.c

@@ -536,6 +536,7 @@ logprintf (enum log_options o, const char *fmt, ...)
   CHECK_VERBOSE (o);
 
   xzero (lpstate);
+  errno = 0;
   do
     {
       va_start (args, fmt);