...calling which had erroneously been dropped in
bdead69d "Add switch for system/internal
npapi.h."  This makes the npsoplugin browser plugin work again.

(Also, init write_fd to -1 instead of 0, so that a missing do_init_pipe does not
accidentally cause writing to write_fd succeed in writing to stdin.)

Change-Id: Iced734512a43c8dfea46088f7ac16f159e7dd807