Re: [REPORT] Static analys warnings

Fix possible overflow when converting, possible negative number to uint16.

postingoff can be -1,when converts to uint16, overflow can raise.
Otherwise, truncation can be occurs, losing precision, from int (31 bits)
to uint16 (15 bits)
There is a little confusion in the parameters of some functions in this
file, postigoff is declared as int, other declared as uint16.

src/backend/access/nbtree/nbtinsert.c
static void _bt_insertonpg(Relation rel, BTScanInsert itup_key,
Buffer buf,
Buffer cbuf,
BTStack stack,
IndexTuple itup,
Size itemsz,
OffsetNumber newitemoff,
int postingoff, // INT
bool split_only_page);
static Buffer _bt_split(Relation rel, BTScanInsert itup_key, Buffer buf,
Buffer cbuf, OffsetNumber newitemoff, Size newitemsz,
IndexTuple newitem, IndexTuple orignewitem,
IndexTuple nposting, uint16 postingoff); // UINT16

regards,
Ranier Vilela