Address Coverity-reported issues.

src/sbbs3/jsexec.c

src/sbbs3/listfile.cpp

src/sbbs3/load_cfg.c

src/sbbs3/logout.cpp

src/sbbs3/mail.cpp

src/sbbs3/mailsrvr.c

src/sbbs3/main.cpp

src/sbbs3/netmail.cpp

src/sbbs3/prntfile.cpp

src/sbbs3/qwktomsg.cpp

src/sbbs3/rechocfg.c

src/sbbs3/sbbsecho.c

src/sbbs3/scfgsave.c

src/sbbs3/services.c

src/sbbs3/str.cpp

src/sbbs3/telgate.cpp

src/sbbs3/tmp_xfer.cpp

src/sbbs3/userdat.c

src/sbbs3/websrvr.c

src/sbbs3/writemsg.cpp