Store write result in dummy variable. (should close #964)

GCC (version 4.8.1, Ubuntu) complains about an unused write()
result, even after a cast to void. There seems to be a long
story behind this (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25509).

As never checking any write() results seems a bit more drastic than
simply making a dummy variable, this commit stores the write()
result in a variable _unusued.