false positive: Uncontrolled data used in OS command

Hi,

We just started using https://github.com/firehol/netdata in LGTM. Thank you!

We found that LGTM reports `cpp/command-line-injection` false positives.

Here is a screenshot:


But the code is the other way around: We use `fgets()` after we run the command, to read the output of the program we execute, like this:

https://lgtm.com/projects/g/firehol/netdata/snapshot/2a7cf3528a14cd50a69af4d75e1441a4b035d231/files/src/cgroup-network.c?#xb0514f82e375bcb6:1