Tidy fill hstv array (src/backend/access/heap/pruneheap.c)

Hi,

The function heap_page_prune (src/backend/access/heap/pruneheap.c)
Has a comment:

"/*
* presult->htsv is not initialized here because all ntuple spots in the
* array will be set either to a valid HTSV_Result value or -1.
*/

IMO, this is a little bogus and does not make sense.

I think it would be more productive to initialize the entire array with -1,
and avoid flagging, one by one, the items that should be -1.

Patch attached.

best regards,
Ranier Vilela