In SPGiST replay, do conflict resolution before modifying the page.

In SPGiST replay, do conflict resolution before modifying the page.

In yesterday's commit 962e0cc71e839c58fb9125fa85511b8bbb8bdbee, I added the
ResolveRecoveryConflictWithSnapshot call in the wrong place.  I correctly
put it before spgRedoVacuumRedirect itself would modify the index page ---
but not before RestoreBkpBlocks, so replay of a record with a full-page
image would modify the page before kicking off any conflicting HS
transactions.  Oops.