ftp/curl: Fix HTTP2

Partially backport upstream commits
70d3a9b6aa69ffdd9435e168463cfabd21e17cd1 and
bef0acaf212a71c782e0b8e8e6c772cc46040356

References:
https://github.com/curl/curl/issues/14923
https://github.com/curl/curl/commit/70d3a9b6aa69ffdd9435e168463cfabd21e17cd1
https://github.com/curl/curl/commit/bef0acaf212a71c782e0b8e8e6c772cc46040356

Approved by: portmgr (blanket, runtime fix)