pgsql: Fix overly-enthusiastic Assert in printing of Param reference ex

Fix overly-enthusiastic Assert in printing of Param reference expressions.

A NestLoopParam's value can only be a Var or Aggref, but this isn't the
case in general for SubPlan parameters, so print_parameter_expr had better
be prepared to cope.  Brain fade in my recent patch to print the referenced
expression instead of just printing $N for PARAM_EXEC Params.  Per report
from Pavel Stehule.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=c6873eac4c33720140240cdbd1a663fecc922c57

Modified Files
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src/backend/utils/adt/ruleutils.c |   15 ++++++++++++---
1 files changed, 12 insertions(+), 3 deletions(-)