BUG/MINOR: stconn: Don't inhibit shutdown on connection on error

BUG/MINOR: stconn: Don't inhibit shutdown on connection on error

In the SC function responsible to perform shutdown, there is a statement
inhibiting the shutdown if an error was encountered on the SC. This
statement is inherited from very old version and should in fact be
removed. The error may be set from the stream. In this case the shutdown
must be performed. In all cases, it is not a big deal if the shutdown is
performed twice because underlying functions already handle multiple calls.

This patch does not fix any bug. Thus there is no reason to backport it.