Without this workaround, NSS re-uses a session cache entry despite the
server name does not match.  This causes SNI host name to differ from
the actual host name.  Consequently, certain servers (e.g. github.com)
respond by 400 to such requests.

Bug: https://bugzilla.mozilla.org/1202264

This reverts commit e6749055.

... since libidn has since been fixed.

I've not mentioned the bug fixes that were shipped in 7.42.1 from the
7_42 branch.

... of an empty file

Bug: https://github.com/bagder/curl/issues/183