bsc/msc: Extension can never be NULL use strlen instead
Fixes: Coverity CID 1040717
diff --git a/openbsc/src/libmsc/vty_interface_layer3.c b/openbsc/src/libmsc/vty_interface_layer3.c
index 923cba0..5b727ef 100644
--- a/openbsc/src/libmsc/vty_interface_layer3.c
+++ b/openbsc/src/libmsc/vty_interface_layer3.c
@@ -62,7 +62,7 @@
subscr->authorized, VTY_NEWLINE);
if (strlen(subscr->name))
vty_out(vty, " Name: '%s'%s", subscr->name, VTY_NEWLINE);
- if (subscr->extension)
+ if (strlen(subscr->extension))
vty_out(vty, " Extension: %s%s", subscr->extension,
VTY_NEWLINE);
vty_out(vty, " LAC: %d/0x%x%s",