netcat: Fix a buffer overflow

The buffer doesn't have the space for the terminating NUL.
Fix it by replacing it with fwrite, as there seems to be little reason
to use fprintf and NUL-terminated string in the first place.

netutils/netcat/netcat_main.c

@@ -99,8 +99,7 @@ int netcat_server(int argc, char * argv[])
       while (0 < avail)
         {
           avail = recv(conn, buf, capacity, 0);
-          buf[avail] = 0;
-          fprintf(fout, "%s", buf);
+          fwrite(buf, avail, 1, fout);
           int status = fflush(fout);
           if (0 != status)
             {