pgsql: psql: Disable %P (pipeline status) for non-active connection

psql: Disable %P (pipeline status) for non-active connection

In the psql prompt, %P prompt shows the current pipeline status. Unlike
most of the other options, its status was showing up in the output
generated even if psql was not connected to a database. This was
confusing, because without a connection a pipeline status makes no
sense.

Like the other options, %P is updated so as its data is now hidden
without an active connection.

Author: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Discussion: https://postgr.es/m/86EF76B5-6E62-404D-B9EC-66F4714D7D5F@gmail.com
Backpatch-through: 18

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4b77282f250103f2ecd54b9f45421c742006317b

Modified Files
--------------
src/bin/psql/prompt.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)