pgsql: Fix out-of-memory error handling in ParameterDescription message

Fix out-of-memory error handling in ParameterDescription message processing.

If libpq ran out of memory while constructing the result set, it would hang,
waiting for more data from the server, which might never arrive. To fix,
distinguish between out-of-memory error and not-enough-data cases, and give
a proper error message back to the client on OOM.

There are still similar issues in handling COPY start messages, but let's
handle that as a separate patch.

Michael Paquier, Amit Kapila and me. Backpatch to all supported versions.

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/affae5e981d624735791ab897ff822118005ab44

Modified Files
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src/interfaces/libpq/fe-protocol3.c | 64 +++++++++++++++++++++++++++++------
1 file changed, 53 insertions(+), 11 deletions(-)