pgsql: Cope with NULL query string in ExecInitParallelPlan().

Cope with NULL query string in ExecInitParallelPlan().

It's far from clear that this is the right approach - but a good
portion of the buildfarm has been red for a few hours, on the last day
of the CF. And this fixes at least the obvious crash. So let's go with
that for now.

Discussion: https://postgr.es/m/20210407225806.majgznh4lk34hjvu%40alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b3ee4c503872f3d0a5d6a7cbde48815f555af15b

Modified Files
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src/backend/executor/execParallel.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)