psql: Set variables from query result on failure when printing tuples

psql: Set variables from query result on failure when printing tuples

SetResultVariables() was not getting called when "printing" a result
that failed (see around PrintQueryResult), which would cause some
variables to not be set, like ROW_COUNT, SQLSTATE or ERROR.  This can be
confusing as a previous result would be retained.

This state could be reached when failing to process tuples in a few
commands, like \gset when it returns no tuples, or \crosstabview.  A
test is added, based on \gset.

This is arguably a bug fix, but no backpatch is done as there is a risk
of breaking scripts that rely on the previous behavior, even if they do
so accidentally.

Reported-by: amutu
Author: Japin Li
Reviewed-by: Tom Lane, Michael Paquier
Discussion: https://postgr.es/m/18134-87126d90cb4dd049@postgresql.org