smpp: Only write the systemd-id if it is not empty
system_id is a char array, which makes the NULL check a tautology,
so we should check with strlen if the string is empty or not.
This is fixing the "write" command of VTY that would otherwise
create a config file that can not be parsed.
diff --git a/openbsc/src/libmsc/smpp_vty.c b/openbsc/src/libmsc/smpp_vty.c
index adea959..a2270e6 100644
--- a/openbsc/src/libmsc/smpp_vty.c
+++ b/openbsc/src/libmsc/smpp_vty.c
@@ -119,7 +119,7 @@
vty_out(vty, "smpp%s", VTY_NEWLINE);
vty_out(vty, " local-tcp-port %u%s", smsc->listen_port, VTY_NEWLINE);
- if (smsc->system_id)
+ if (smsc->system_id && strlen(smsc->system_id) > 0)
vty_out(vty, " system-id %s%s", smsc->system_id, VTY_NEWLINE);
vty_out(vty, " policy %s%s",
smsc->accept_all ? "accept-all" : "closed", VTY_NEWLINE);