pgsql: Fix fallback behavior when server sends an ERROR early at startu

Fix fallback behavior when server sends an ERROR early at startup

With sslmode=prefer, the desired behavior is to completely fail the
connection attempt, *not* fall back to a plaintext connection, if the
server responds to the SSLRequest with an error ('E') response instead
of rejecting SSL with an 'N' response. This was broken in commit
05fd30c0e7.

Reported-by: Jacob Champion
Reviewed-by: Michael Paquier
Discussion:
https://www.postgresql.org/message-id/CAOYmi%2Bnwvu21mJ4DYKUa98HdfM_KZJi7B1MhyXtnsyOO-PB6Ww%40mail.gmail.com
Backpatch-through: 17

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/c95d2159c1dd3f269383a9bd830e1c804dba34c8

Modified Files
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src/interfaces/libpq/fe-connect.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)