Thread: pgsql: Reproduce debug_query_string==NULL on parallel workers.

Reproduce debug_query_string==NULL on parallel workers.

Certain background workers initiate parallel queries while
debug_query_string==NULL, at which point they attempted strlen(NULL) and
died to SIGSEGV.  Older debug_query_string observers allow NULL, so do
likewise in these newer ones.  Back-patch to v11, where commit
7de4a1bcc56f494acbd0d6e70781df877dc8ecb5 introduced the first of these.

Discussion: https://postgr.es/m/20201014022636.GA1962668@rfd.leadboat.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f90e80b9138355a51d2d5b5b63e1f89c4ba53325

Modified Files
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src/backend/access/heap/vacuumlazy.c | 28 +++++++++++++++++++---------
src/backend/access/nbtree/nbtsort.c  | 25 +++++++++++++++++--------
2 files changed, 36 insertions(+), 17 deletions(-)