Fix a valid warning that some compilers warned
Fix a valid warning that some compilers warned

And it's a good idea not to ignore fwrite's return value I suppose.

Signed-off-by: Brandon Low <a52c3838af000af4c7c0bc518c135eded66d273a@lostlogicx.com>

gevaerts/bup,jbaber/bup,tjanez/bup,pombredanne/bup,mhoeher/bup,mhoeher/bup,apenwarr/bup,jbaber/bup,tjanez/bup,pombredanne/bup,apenwarr/bup,jbaber/bup,pombredanne/bup,mhoeher/bup,pombredanne/bup,ToxicFrog/bup,pombredanne/bup,tjanez/bup,tjanez/bup,jbaber/bup,tjanez/bup,jbaber/bup,apenwarr/bup,ToxicFrog/bup,tjanez/bup,ToxicFrog/bup,mhoeher/bup,jbaber/bup,mhoeher/bup,ToxicFrog/bup,gevaerts/bup,pombredanne/bup,mhoeher/bup,apenwarr/bup,gevaerts/bup,gevaerts/bup,gevaerts/bup,ToxicFrog/bup