fix(js): scan fetch record limit

[genaris]

There is an unnecessary chunk variable (inherited from previous Indy SDK implementation in AFJ) that is preventing fetchAll to retrieve all records when they are more than PAGE_SIZE. As a result, a given Scan cannot return more than 32 entries.

Simply checking for listHandle (scanNext return value) validity seems to be enough to determine if there are no more matching records.

[genaris]

Isn't the 256 here to prevent you from retrieving too many records and messing stuff up? Or do you we want to make that a responsiblity of the caller?

I think in this case is a bit different from Indy SDK because scanNext does not receive a chunk size: instead, it is retrieving at most 32 records per call (in Indy we used fetchWalletSearchNextRecords, which received a count parameter). So the loop will be executed until specified limit is reached or a scanNext call returns 0 records.