Fix list unmarshal bug

[crufter]

I've discovered a bug in list where some values from previous rows lingered, ie:

Row ID	Col A	Col B
ROW 1	Val A1	Val B1
ROW 2		Val B2

So list returned Val A1 for both row 1 and row 2.

I suspect the json output from the airtable api omits empty strings, and with the key missing the reused tempsRecordsHolder is not being updated.

To avoid that, I moved its initialisation inside the recursive function recursivelyListRecordsAtOffset. That fixed my problems.

Edit: I've just read the comments above the code I've modified again and it made me doubt myself. Have to give this a second thought.

Edit2: I've just ran a second round of tests and the bug is definitely there and this patch definitely fixes it. Will try to come up with a repro.