FileREader: throw if file is nonexistent

8 jobs for master in 3 minutes and 21 seconds (queued for 1 second)
Status Name Job ID Coverage
  Compile
passed cmp:cc7-gcc #811923
docker

00:00:59

passed cmp:cc7-llvm #811924
docker

00:01:17

passed cmp:mac1013-clang #811925
mac

00:00:52

passed cmp:slc6-gcc #811921
docker

00:02:03

passed cmp:slc6-llvm #811922
docker

00:00:55

 
  Format
passed fmt:centos7-llvm-format #811927
docker

00:00:20

passed fmt:slc6-llvm-format #811926
docker

00:00:11

 
  Documentation
passed cmp:usermanual #811928
docker

00:00:57