pgsql: Fix some memory leaks associated with parsing json and manifests

Fix some memory leaks associated with parsing json and manifests

Coverity complained about not freeing some memory associated with
incrementally parsing backup manifests. To fix that, provide and use a new
shutdown function for the JsonManifestParseIncrementalState object, in
line with a suggestion from Tom Lane.

While analysing the problem, I noticed a buglet in freeing memory for
incremental json lexers. To fix that remove a bogus condition on
freeing the memory allocated for them.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/661ab4e185784db79c194b5758555b1db3f30483

Modified Files
--------------
src/backend/backup/basebackup_incremental.c | 3 +++
src/bin/pg_combinebackup/load_manifest.c | 3 +++
src/bin/pg_verifybackup/pg_verifybackup.c | 3 +++
src/common/jsonapi.c | 21 ++++++++++-----------
src/common/parse_manifest.c | 13 ++++++++++++-
src/include/common/parse_manifest.h | 1 +
6 files changed, 32 insertions(+), 12 deletions(-)