not exist), set the user->number to 0 before returning as many callers of this
function do not check the return value, just the value of user->number after
it returns (ugh). This problem was discovered when running a fresh install,
typing "1" at the Login prompt and immediately getting a "Time's Up" message
and a disconnect - only happens when there's no data/user.dat file.

getnodedat() - don't try to unlock the node.dab file unless the read() fails.
When using the MSVC2017 CRTL, an unlock() of a region that was not previously
locked is a blocking call causing major slowness in the MSVC2017 build.

putmsgptrs() - cleans up obsolete sections in the data/user/*.subs files now.
So if you go from say 10,000 sub-boards to 2,000, it won't have to load and
search through the extra 8,000 invalid subs (once the file is re-written upon
log-off). This requires an updated xpdev build (for iniAppendSectionWithKeys)

fixmsgptrs() - if the msgbase index can't be opened or the last index record
cannot be read (e.g. there isn't one), insure the msg-scan pointer value is
set to 0 (not ~0).