Don't warn about not sending a socks reply if we get a write error

If we get a write error on a SOCKS connection, we can't send a
SOCKS reply, now can we?

This bug has been here since 36baf7219, where we added the "hey, I'm
closing an AP connection but I haven't finished the socks
handshake!" message.  It's bug 8427.

changes/bug8427

@@ -0,0 +1,5 @@
+  o Minor bugfixes:
+    - If we encounter a write failure on a SOCKS connection before we
+      finish our SOCKS handshake, don't warn that we closed the
+      connection before we could send a SOCKS reply. Fixes bug 8427;
+      bugfix on 0.1.0.1-rc.

src/or/connection.c

@@ -3286,6 +3286,10 @@ connection_handle_write_impl(connection_t *conn, int force)
     if (result < 0) {
       if (CONN_IS_EDGE(conn))
         connection_edge_end_errno(TO_EDGE_CONN(conn));
+      if (conn->type == CONN_TYPE_AP) {
+        /* writing failed; we couldn't send a SOCKS reply if we wanted to */
+        TO_ENTRY_CONN(conn)->socks_request->has_finished = 1;
+      }
 
       connection_close_immediate(conn); /* Don't flush; connection is dead. */
       connection_mark_for_close(conn);