Find dangling membership roles in pg_dumpall

Hello,

pg_dumpall.c has a function dumpRoleMembership() which dumps all
membership roles. This function includes a piece of code which checks
if the membership tree has an open end which can't be resolved.
However that code is never used.

The variable prev_remaining is initially set to 0, and then never changed.
Which in turn never executes this code:

if (remaining == prev_remaining)

because the loop is only entered while "remaining > 0".

The attached patch fixes this problem, and updates prev_remaining inside
the loop.

Co-Author: Artur Zakirov <zaartur(at)gmail(dot)com>
who reviewed the patch.

Regards

--
Andreas 'ads' Scherbaum
German PostgreSQL User Group
European PostgreSQL User Group - Board of Directors
Volunteer Regional Contact, Germany - PostgreSQL Project