liblogcat: redirect logcat output correctly for -Q

The -Q option is used in emulator and it fails to redirect the
output of logcat to the desired file.

This CL fixes that problem.

There is no gTest because of /proc/cmdline sniffing for this option.
manually tested on /dev/qemu_pipe inside emulator

Test: manual
Bug: 35326290
Change-Id: I282da685e90450aadb2a989a0517dc3b1bb6634d