Replace sprintf() calls with snprintf()

src/sbbs3/atcodes.cpp

src/sbbs3/chat.cpp

src/sbbs3/con_hi.cpp

src/sbbs3/con_out.cpp

src/sbbs3/exec.cpp

src/sbbs3/execfile.cpp

src/sbbs3/execfunc.cpp

src/sbbs3/execmisc.cpp

src/sbbs3/execmsg.cpp

src/sbbs3/execnet.cpp

src/sbbs3/fido.cpp

src/sbbs3/file.cpp

src/sbbs3/getnode.cpp

src/sbbs3/js_bbs.cpp

src/sbbs3/js_console.cpp

src/sbbs3/js_system.c

src/sbbs3/listfile.cpp

src/sbbs3/login.cpp

src/sbbs3/mail.cpp

src/sbbs3/main.cpp