pgsql: fix u16 overflow in query data_row

pgsql: fix u16 overflow in query data_row

Found by oss-fuzz with quadfuzz.

Cf https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=63113

According to PostgreSQL documentation the maximum number of rows can be
the maximum of tuples that can fit onto max u32 pages - 4,294,967,295 (cf
https://www.postgresql.org/docs/current/limits.html). Some rough
calculations for that indicate that this could go over max u32, so
updating the data_row data type to u64.

Bug #6389