Add missing set_in_callback around callback.

[taiyu-len]

Happened to find a callback not surrounded by the Curl_set_in_callback functions.

[bagder]

Thanks!

[michaelforney]

I noticed that after upgrading to curl 7.65.0, netsurf isn't working with HTTP redirects, and I bisected it down to this commit.

After some investigation, it looks like this is because netsurf is calling curl_multi_add_handle from within the CURLOPT_WRITEFUNCTION callback upon seeing a 3xx HTTP code.

I guess this is the sort of thing this commit is intended to prevent? Just wanted to check before submitting a netsurf bug report.

[jay]

After some investigation, it looks like this is because netsurf is calling curl_multi_add_handle from within the CURLOPT_WRITEFUNCTION callback upon seeing a 3xx HTTP code.

I guess this is the sort of thing this commit is intended to prevent?

Yes that was the intention, please refer to the discussion in #2302.