[Gelbooru] Trying to download a tag with a lot of images caps out at 20 thousand images

[Kelhsy]

Trying to download a tag from gelbooru but the download fails after 20000 images are downloaded, here's the --verbose output:

[gelbooru][error] An unexpected error occurred: AttributeError - 'dict' object has no attribute 'attrib'. Please run gallery-dl again with the --verbose flag, copy its output and report this issue on https://github.com/mikf/gallery-dl/issues .
[gelbooru][debug]
Traceback (most recent call last):
File "requests\models.pyc", line 910, in json
File "json_init_.pyc", line 348, in loads
File "json\decoder.pyc", line 337, in decode
File "json\decoder.pyc", line 355, in raw_decode
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "gallery_dl\extractor\gelbooru.pyc", line 40, in _pagination
File "gallery_dl\extractor\gelbooru.pyc", line 25, in _api_request
File "requests\models.pyc", line 917, in json
requests.exceptions.JSONDecodeError: [Errno Expecting value] Too deep! Pull it back some. Holy fuck.: 0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "gallery_dl\job.pyc", line 79, in run
File "gallery_dl\extractor\booru.pyc", line 29, in items
File "gallery_dl\extractor\gelbooru.pyc", line 46, in _pagination
AttributeError: 'dict' object has no attribute 'attrib'

[mikf]

Fixed in e2be199.

As the commit message says, the 20k limit was already fixed in a previous commit, but I managed to break that again when updating to Gelbooru's changed API responses.