fix some unused variables and comparison of different types

src/common/fdset.c

src/common/queue.c

src/knot/ctl/knotc_main.c

src/knot/main.c

src/libknot/rrset-dump.c

src/libknot/sign/dnssec.c

src/libknot/sign/key.c

src/libknot/util/debug.c

src/libknot/util/debug.h

src/utils/common/netio.c

src/utils/common/params.c

src/utils/host/host_params.c

src/utils/nsupdate/nsupdate_exec.c

src/utils/nsupdate/nsupdate_params.c

src/zscanner/file_loader.c

src/zscanner/scanner.c

src/zscanner/scanner_body.rl

src/zscanner/scanner_functions.c

src/zscanner/test/processing.c

src/zscanner/test/processing.h