Low: main: fix hypothetical file path double traversal discrepancy

Now we check retrospectively once the file held firmly, i.e.,, there's
a single path traversal only, just in case.

Since fstat appears just as standards compliant as mere stat, there's
nothing (not even lightness on resources/system limits since opening
the file is on the likely, happy path).precluding such an arrangement.

Discovered-by: static analysis/Coverity
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>