libfdisk: fix possible memory leak [clang-analyze]

Signed-off-by: Karel Zak <kzak@redhat.com>
fsck: uninitialized argument value [clang-analyze]

Signed-off-by: Karel Zak <kzak@redhat.com>
lib/ismounted: more robust buffer usage [clang-analyze]

Signed-off-by: Karel Zak <kzak@redhat.com>