Since Revision 1.36 of load/fidocfg.js (Jan-8-2019), a blank/unconfigured

BinkP session password ("SessionPwd") in sbbsecho.ini would cause BinkIT/BinkP
to behave as though a session password was specified. The reason for the change
to fidocfg.js (specifying a default value for "SessionPwd" as a blank string)
was to force the return value to a string so that numeric passwords were not
returned as numbers but rather strings.
The binkit.js and binkp.js code assumed that a blank password would be
'undefined' and not a blank string.
This commit changes binkit.js and binkp.js to treat all of the following
session password values as "no password" with respect to BinkP:
- false
- undefined
- blank string ('')