libctrl: only free() msgb if it was alloc()ed
Before this patch a SIGABRT was caused when doing e.g.:
$ ncat 127.0.0.1 4249
^C
diff --git a/openbsc/src/libctrl/control_if.c b/openbsc/src/libctrl/control_if.c
index 8198ae6..d081342 100644
--- a/openbsc/src/libctrl/control_if.c
+++ b/openbsc/src/libctrl/control_if.c
@@ -208,7 +208,7 @@
struct ctrl_connection *ccon;
struct ipaccess_head *iph;
struct ipaccess_head_ext *iph_ext;
- struct msgb *msg;
+ struct msgb *msg = NULL;
struct ctrl_cmd *cmd;
struct ctrl_handle *ctrl = bfd->data;