sgs_iface: fix nullpointer dereference

The function sgs_tx() is using the sgs connection pointer as context,
even though it has done a check for a nullpointer in the line before.
This is very prone to lead into a segfault when the SGs connection dies.

Change-Id: I88b95e3f8cd35241ad68f08d94c6ad7067b842e6
Related: OS#3859
1 file changed