BUG #15627: libpq memory leak

The following bug has been logged on the website:

Bug reference:      15627
Logged by:          ice ice
Email address:      icegood1980@gmail.com
PostgreSQL version: 11.1
Operating system:   Ubuntu 18.04.1 LTS
Description:

PQisBusy has memory leak with next valgrind stack:

  1: malloc in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so
  2: PQmakeEmptyPGresult in
/opt/src/postgres/src/interfaces/libpq/fe-exec.c:146
  3: getRowDescriptions in
/opt/src/postgres/src/interfaces/libpq/fe-protocol3.c:492
  4: pqParseInput3 in
/opt/src/postgres/src/interfaces/libpq/fe-protocol3.c:293
  5: parseInput in /opt/src/postgres/src/interfaces/libpq/fe-exec.c:1747
  6: PQisBusy in /opt/src/postgres/src/interfaces/libpq/fe-exec.c:1764

The problem is that if PQisBusy doesn't revoke memory for item

/* Status for asynchronous result construction */
    PGresult   *result;            /* result being constructed */

in struct pg_conn