libpq: Fix wrong connection status on invalid "connect_timeout"

Greetings,

libpq since PostgreSQL-12 has stricter checks for integer values in
connection parameters. They were introduced by commit
https://github.com/postgres/postgres/commit/e7a2217978d9cbb2149bfcb4ef1e45716cfcbefb
.

However in case of "connect_timeout" such an invalid integer value leads
to a connection status other than CONNECTION_OK or CONNECTION_BAD. The
wrong parameter is therefore not properly reported to user space. This
patch fixes this by explicit setting CONNECTION_BAD.

The issue was raised on ruby-pg: https://github.com/ged/ruby-pg/issues/302

It originally came up at Heroku:
https://github.com/heroku/stack-images/issues/147

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Kind Regards,
Lars Kanis