pgsql: Fix parallel index scan hang with deleted or half-dead pages.

Fix parallel index scan hang with deleted or half-dead pages. The previous coding forgot to release the scan before seizing it again, leading to a lockup. Report by Patrick Hemmer. Diagnosis by Thomas Munro. Patch by Amit Kapila. Discussion: http://postgr.es/m/CAEepm=2xZUcOGP9V0O_G0=2P2wwXwPr

pgsql: Fix parallel index scan hang with deleted or half-dead pages.

Fix parallel index scan hang with deleted or half-dead pages. The previous coding forgot to release the scan before seizing it again, leading to a lockup. Report by Patrick Hemmer. Diagnosis by Thomas Munro. Patch by Amit Kapila. Discussion: http://postgr.es/m/CAEepm=2xZUcOGP9V0O_G0=2P2wwXwPr