Attached.

Example based on [1] that crashes without this fix can be found here:

https://gist.github.com/7bc07da1dcd02e01c2fbb28cbaa81420

Input is from git's tests (2.17.0), and fixes tests when using
noxcuse-based iconv utility and musl's iconv implementation.

Well, *almost*.   At least no more crashing :).  One final test
involving autosquash fails-- I believe due to a comparison breaking
due to unexpected shifts in ISO-2022-JP encoding (as described in [2])
but I'm not sure of details just yet.  Neat to get this far!

~Will

[1] http://www.openwall.com/lists/musl/2017/05/03/1
[2] http://www.openwall.com/lists/musl/2014/11/09/1