Changes

stream_cli: Assert reentrant disconnect_cb() never happens

This should in fact already be guarded by early return in
stream_cli_close() setting and checking for CLOSED state, but it doesn't
hurt having this assert which also provides extra information to the
reader.

Change-Id: I9a12d76e27dce2b31a2aa993b70cbed30bdea7f2

stream_cli: Explicitly ignore return code of stream_cli_close

Make coverity happy.
We don't really case about th return code of the stream_cli_close()
function in the code path, since the return value is only used
internally/privately in the object and there's no further access/use of
the object after calling it in osmo_stream_cli_close().

Take the chance to update syntax of one return code check to match more
similarly other return checks of the same function.

Related: Coverity CID#435092
Change-Id: Ia6c9e3ca3af08b386f017460b0a0210ed756a929