fcgi: handle memory allocation failure in append_content
fcgi: handle memory allocation failure in append_content

h2o_buffer_try_reserve does not abort on mmap failure, therefore
check the return value and bubble up the error.

yannick/h2o,devnexen/h2o,devnexen/h2o,deweerdt/h2o,cwyang/h2o,h2o/h2o,cwyang/h2o,h2o/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,yannick/h2o,deweerdt/h2o,yannick/h2o,deweerdt/h2o,devnexen/h2o,yannick/h2o,cwyang/h2o,cwyang/h2o,devnexen/h2o,h2o/h2o,deweerdt/h2o,h2o/h2o,cwyang/h2o,yannick/h2o,deweerdt/h2o,cwyang/h2o,devnexen/h2o,yannick/h2o,cwyang/h2o,devnexen/h2o,h2o/h2o,h2o/h2o,h2o/h2o,h2o/h2o,deweerdt/h2o,deweerdt/h2o,deweerdt/h2o,deweerdt/h2o,cwyang/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,yannick/h2o