Fix output token and GSS context leaks in TKEY/GSS-API error paths

Fix output token and GSS context leaks in TKEY/GSS-API error paths

In dst_gssapi_acceptctx(), rename outtoken to outtokenp (matching BIND
convention for output pointer parameters) and free the allocated output
token buffer on error in the cleanup path.

In process_gsstkey(), route the empty-principal error path through
cleanup via CLEANUP() instead of returning early, so that the output
token, GSS context, and TSIG key are all freed consistently by the
existing cleanup block.

(cherry picked from commit f2240d2d06a1a68b622bd6b00a52c6fe4274426d)